I got into a conversation with a friend recently about all of our alts and, specifically, remembering each toon's (and each class') abilities, rotation and keybinds.
I love my alts and love playing different classes and different roles. I also love playing all the different types of roles - I have a toon for each healing class and spec, and almost all the tank classes (though I'm saving my warrior for a worgen in Cata). I'm a little behind in the dps classes (I never could get a lock past level 20, and debating whether to keep poking my mage up in levels or wait for Cata and another night elf) but I've had a ton of fun with them as well.
This many toons results in a ton of different abilities and rotations and of your keybinds and UI between each toon. The biggest potential issue seems to be how to keep track of it all!
The most useful thing I've found to help myself manage all my toons is keeping key and similar abilities to consistent key binds and setups.
For example; all of my tanking toons (or toons with tanking abilities, such as my druid's bear form) have their primary taunt bound to the same key. All of my night elves have their shadowmeld on the same key (indeed, all of my toon racials are on the same key). Similar abilities also get similar bindings. My bear form Bash is on the same key as my pally Hammer of Justice, my rogue's Kick has the same bind as my DK's Mind Freeze. Damage mitigation abilities (Icebound Fortitude, Divine Protection, Barkskin) all have consistent binds as well.
All of my healing toons have consistent bindings on my Vudho. While not necessarily the same binds, they're correlations which make sense to me, which is key. The beauty of Vuhdo allowing me to save different profiles for one toon's dual spec has let me put my priest's Penance (disc) and Circle of Healing (holy) to the same bind - connected, in my mind, as each spec's 'special'. Similarly, my priest's Pain Suppression and Guardian Spirit are also on the same bind. Heals like Nourish, Flash Heal, Healing Wave and Holy Light all also have the same binds.
In cases where I have multiple toons of the same class, I make sure they all have the same binds as each other.
The key with all of this is that, despite being different classes with different abilities, the core setup remains consistent. This helps ensure that no matter which toon I'm on, my reactions will be quick (particularly for important abilities like certain heals, damage mitigation tools, taunts, interrupts, etc) and I won't be second-guessing. Particularly in a progression raid setting (and also in PVP, really), a second's hesitation can make the difference between a win and a loss.
The most important thing I think though is a clean UI and bind setup that makes sense to you! Part of the reason I don't use any addons which change my action bar locations is due to this - I've finally gotten my setup in such a way that it is logical to me and now has natural reactions, so I don't dare mess with it! Keeping consistencies across different toons is definitely helpful, and it will make switching between alts that bit easier!