From a "Day 2 systems panel" thread:

Mastery system

* There are too many talents right now and a lot of them are boring and just give passive bonuses. (1% hit bonus, etc ...)
* The goal is to make talents more fun and useful, Body and Soul or Juggernaut are a good example.
* The old passive bonuses will be automatically added to your character through the Mastery system as you spend more points in a talent tree. Spending a lot of points in Fury will give you extra crit, etc ... this will be implemented for all classes.
* Mastery bonuses will lower energy cost, increase your armor penetration, etc ...
Hmm, so that's what's happening with hit/crit/mp5/etc. Wonder how this will affect hybrid specs. Example: elemental mages. Used to be able to sneak in mana regen from arcane and then do split frost/fire. If it requires deep spec in a line to make that line's spells efficient, will it completely neuter using other schools' spells effectively? Be interesting to see how that turns out.