The other day in the Battle.net forums, Bashiok had shed a little insight as to how keybindings will work in Diablo 3, along with RMB (right-mouse-button) skill swaps.
From his post it sounds like players will have access to 8 character functions on the fly. The UI will display 5 action bar slots which will be bound to keys 1-5 by default, plus the left and right mouse buttons, as well as a right mouse button hot swap key. Currently this key is x, but it can be re-assigned, along with the default 1-5 keybinds as well.
Quote from Bashiok
Hrm, I’m confused, I think you may be too. Let me explain more fully how this functions now.
On the UI you’ll see spots for 5 skills, by default bound to 1-5 number keys. You can rebind these if you want. You’ll also have left mouse button and right mouse button skill slots. If you hit the X key it’ll swap the right mouse key to another skill slot. The swap key (X) can also be bound to a different key if you want, Tab, if you like it old school. When you swap to that slot it behaves exactly the same, and is still used by clicking the right mouse button.
It’s essentially a way to get this function out of sight for the people it confused, it frees up some UI real estate, and we offer some better functionality in that the swap key can be customized so you don’t accidentally hit it when you don’t want to.
For me, I like T because it’s a quick travel for my index finger as it rests on 5, for others, you’re free to rebind as you’d like.
As I’d mentioned, it seems as if there will be 8 available actions, but it’s possible that the right-mouse-button hot swap may be related to one of the skills in action bar slots 1-5. It’s hard to discern for certain from his post, but I’m guessing that the hot swap RMB skill will be a unique one, giving us a total of 8 actions.