If I had 5 copper for every time I tried to use a class specific ability while playing another class I'd have epic flying on all five of my flight capable toons instead of just the one (and I only got that one through a guild fundraiser).
It was quite obvious to me that I'd never stop trying to blink on other toons after playing my mage for a while. I'd still fall back to a feral DPS rotation when I wasn't paying attention on my rogue. It is just how I am and there isn't any fighting it.
So the next best thing is to make it so it won't matter! Put similar abilities in the same places and suddenly an altaholics weakness becomes an advantage. Easier said than done, but over the past few weeks I have gotten pretty close.
This unification process also played a beneficial role in getting away from clicking and moving toward more key bindings. What better time to remap some muscle memory than when it will apply to all toons.
I started the move to key bindings in small steps weeks before I thought of unifying across toons. I can't reach 7-9,0,-,= so I remapped those action bar slots to Q, E, 7-9,0. I do all my turning and strafing with the mouse anyway so it was two more free buttons that are really easy to reach from WASD. I rearranged my bars on a couple toons to compensate for the new hot keys. Next I took a liking to F1-F5 and bound those to my lower left additional bar.
I was a notorious clicker so of course I had all four additional toolbars up all the time. :)
Some time later I still couldn't reach 7-9,0 so I bound those to some more nearby letters: R, F, T and G. I hadn't used any of these keys for their original functions for over a year so I wouldn't miss them. I've used /r to reply since forever because I just associate / with the chat frames. I've always done all my focus setting through macros and assisting someone blindly just doesn't work for me. I use pitbull for my unit frames which also display target frames which I grab targets off of when I need too. In any case it didn't impact my play style, but it might be more of an issue for some.
I had a vague sense of similarity between toons at this point which just kind of happened. The only key that really had a defined purpose was E which I used for AOE type abilities. Other than that it was whatever worked best.
In comes the unification movement! I started up a spreadsheet with a template outlining all my 6 standard action bars and started defining slots to certain generic abilities. I didn't get very many filled in so I just made a few copies and started plugging in actual abilities for a few characters I played most.
Through an interactive back and forth process the template started to take shape and today it is in a pretty good place. Still a work in progress though and probably will be until I play a max level toon of every class/spec and even then I'll end up tweaking something.
What keys do I have bound?
So right now I have F1 through F12 bound to my lower left additional action bar right above the default action bar. I can't reach F6-F12, but I wasn't using them for anything else and I figured I might take my hand off the mouse once in a blue moon and learn to use them.
On my default action bar I have 1-6, Q, E, R, F, T and G. I use ~ for push to talk over vent and the rest of the keys are still bound to their default actions with the exception of V and B. I have those two keys bound to action bars on the far right. They were the first two keys bound as a direct result of my template, I am thinking of using C as well if I find a reason.
What do I have bound where?
I use F1 through F3 somewhat flexibly as short term buffs and debuffs. Per encounter type abilities in DND terms. For my druid this is feral faerie fire, berserk, entangling roots/nature's grasp (with alt modifier). For my hunter: rapid fire, readiness and misdirection. DK: plague strike (I have a macro to put up diseases and use this as a backup in case the castsequence fails for some reason), horn of winter and hysteria. Resto shaman: water shield, earth shield and earthbind totem. Enh shaman: lightning shield, feral spirit and earthbind totem.
A bit verbose, but I think that gives a pretty good idea of the types of differences between classes when the template is somewhat vague. The next couple keys are more static in their function.
F4 is used to break snares, crowd control and/or movement impairing effects. A power shift macro for my druid to flip back into whatever form I am in, every man for himself for my humans, tremor totem for my shaman, escape artist on my gnome, etc. A common key to hit when I want to get out of something.
F5 is my emergency damage mitigation type ability. Barkskin for my druid, evasion for my rogue, deterrence on my hunter, stoneclaw totem on my shaman, etc. Yes stoneclaw totem isn't exactly the same like the others are, but the idea is that if I pull something I shouldn't it will buy me some time.
1-4 and Q make up my primary abilities for whatever class/spec I am using. These are the abilities you use multiple times every single fight. If you have a rotation (priority based or not), this is it. 3 and 4 are easiest for me to hit while moving around simultaneously so that is where I stick highly used abilities and/or abilities with an orientation requirement like having to be behind your target. Still I can only strafe left at the same time leading to lots of dizzying clockwise maneuvers when called for. 1 and Q come in second for ease of access and 2 takes my finger off the forward button so I usually stick something I don't use often or requires me to stand still there. I don't like standing still. :)
5 is another ability used pretty much every fight, but not as often. This would be a finishing move or something with a longer cooldown. For my druid this is rip, my hunter uses kill shot and my rogue uses rupture. For some healer love I use this for swiftmend on my druid and earth shock on my shaman (yes I do DPS when I can as a healer).
For tanks I use 4 and/or 5 as taunts.
One of my favorite keys is E! It's my spamming AOE key of doom. Arcane explosion on my mage, swipe on my druid, fan of knives one day on my rogue. Some classes have boring AOE (read not spammable), multi-shot for my hunter and chain lightning for my shaman.
Speaking of AOE you might be asking what about blizzard, volley, hurricane, etc. These abilities require you to target an area on the ground, generally near the middle of your screen. I stick these abilities on the right side of my lower left additional action bar (bound to F12, F11, etc). Since I have to move my mouse over there to target the ground anyway I just keep these abilities close and click twice to use them.
6 is also hard to reach, harder than any of my other keys I use on my keyboard. I use this for start of fight type abilities: stealth, hunter's mark, death grip, frostbolt (mage is leveling), etc. Pretty much a reflex when I am going to start trouble to hit 6.
R bring goes back to a more single purposed key mapping scheme. I use R to charge, blink, shadowstep and to blow the crap out of corpses on my DK. Some classes don't have a charge or blink like ability so R becomes just another relatively easy key to bind a frequently used ability to. In this case since R is very close to E I use it as a secondary AOE ability on my death knight.
Keeping similar abilities together on a class to class basis is just as important if not more so than keeping things the same between classes.
F is a stun, slow, snare ability. Bash for bears, maim for cats, kidney shot for rogues, frost shock for shamans, concussive shot for hunters, hammer of justice for pallies etc.
T is a spell interrupt. Kick, mind freeze, counterspell, silencing shot, etc. This and F are pretty important and beneficial to keep constant across all classes and specs. Having a reflexive stun and interrupt speeds reaction times for abilities where time matters.
The last slot on the default action bar I use for an aggro drop. Feign, feint, cower, etc. Classes that don't have such an ability like my death knight I have a second spell interrupt here. My shaman's spell interrupt is also an agrro reduction ability so I stuck a dispel ability here.
My last two key binds are V and B. I use V for a mana regen ability: aspect of the viper for my hunter, mana tide totem for my shaman, innervate for my druid, shamanistic rage for my shaman's DPS spec. For classes that don't use mana I wing it. For my dk this summons my ghoul and then sacrifices it for health (blood dks use ghouls for health pots). I was planning on using this for an energy drink on my rogue.
B I use for my most often cast long term buff. Mark/Gift of the wild on my druid, aspect of the dragonhawk on my hunter, weapon enchants and poisons for my shaman and rogue.
Just as an added note of awesomeness, I just started using B and V on my hunter last night and boy was that slick for flipping between dragonhawk and viper when getting mana. I hardly had to click anything at all and that was proof to myself right there that keybindings were improving my game play.
The rest of my unification is all clicking and rarely/intermittently used abilities. I stick things I use more towards the ends of bars where they are easier to find. I stick all my buffs at the top of my two additional action bars on the right side. This includes the new drums my leatherworker can make. In the middle I have engineering stuff on my engineers, quest items, and more or less random stuff. I keep most the class unique/specific utility abilities on the lower right additional action bar nice and spread out if I can. That leaves a big hole in the middle of the right side action bars on most toons.
At the bottom right side I have a nice big block of stuff that stays pretty constant between all toons: mount, hearth, rez, health regen/bandage, drink, eat, mana regen, healthstone, mana potion, health potions and my two trinkets.
For professions and some abilities that are rarely if ever used I use the second action bar accessible by hitting the up/down buttons on the right side of the defaults action bar. The only class I am using this for abilities is my hunter. Tame beast and beast lore are used like never, but I don't want to look through my spell book when I want them.
Thoughts action bar complexity by class?
From the worst (hardest to set up) action bar experience to the best (easiest to set up).
Hunters suck! Especially if you are an engineer. You will fill every single action bar slot and still want more. That is with a very high comfort level with macros. If you don't use macros you cannot play a hunter correctly, sad but true. That must be the root cause of the huntard phenomenon.
Warlocks are the caster versions of hunters. Well maybe not that bad, but they certainly have a lot of abilities. A moderate use of macros goes a long way in keeping thing clean. I've only recently hit 20 and and am little overwhelmed, hopefully it doesn't get worse.
Rogues are pretty clean, but a lot of utility stuff that you almost want to bind, but just don't have the room. They are worse than hunters in that respect, but overall there is lots of room to go around to click stuff.
I don't play a priest, but I am guessing they fall somewhere around here.
Shamans suffer from the same problems as hunters with just too much if you stick it all on you bars, but not quite as bad. Using a totem managing add-on like totem timers or even the default totem manager blizzard stuck in cleaned things up considerably. You don't need to keep all your buff totems on your bars, just a few situational ones.
Druids with all their abilities and complexities are very surprisingly simple when it comes to action bars. Hiding a lot of abilities inside different forms really cleans things up for what you see at any given time. Going to have to use some macros if you plan on going feral DPS since the cat form has more abilities than can fit on a bar. Other specs are fine without, but better with macros.
Death knights with proper macros clean up real nice. Without macros they still aren't terrible. Abilities like rune strike which when not macroed must be constantly monitored and are just annoying.
I don't play a warrior, but I am guessing they fall around here.
Mages have a lot of stuff, but a lot of it isn't useful depending on spec, once you figure out what is what things get a lot simpler. Not much need for macros here. All those teleports/portals to different cities will tank their toll with time.
Paladins have so few abilities and so many keys to bind them too. Well actually they have about as many as other classes (most of which are buffs), but a very small subset is used at any given time.