Mar 1st 2010 5:52PM Mastery, I believe, is going to be tied to the fact that you will get certain stats depending on how far down your respective tree you went.
Back in Blizzcon, I believe, they stated that the rogue tree, for instance, would gain to stats depending on the tree. Assassin would get +% to poisons and AP, combat would get +haste and AP, etc.
Assuming arcane will be a haste tree, I think mastery might be that it flat out increases the benefit you get from your tree itself. If so, it'd be interesting to see how they might balance whether you get more dps from "mastery" or "haste" stat.
Mar 1st 2010 5:48PM They didn't say SP was going away entirely, you just will never see it on gear (weapons excepted). Similarly, like with AP going away, they want the SP mechanic, but since all your gear always will have int and SP on it, why not just get your SP FROM said int?