Blizzard devs have posted a lot of new information about updates coming to both the Class and Mastery systems with the arrival of the Cataclysm expansion. Basically, the changes are:
The Vision: Talent trees will be reduced to 31 points with the aim that players will purchase the points as they level in a meaningful way. The speed that Talent Points are awarded will be slowed. Blizzard has trimmed away or altered the 'lame' talents that fall between the ones most popular with players. Devs are also looking at altering the mandatory purchase of PvP points.
Specialization: Specialization, or at least the feel of specialization, will occur much faster. The goal is to allow players to feel that the points are well-spent and immediately noticeable. At level 10, players will be asked to choose their specialization and be awarded passive bonuses for that skill and a 'signature ability' that used to come much further down the line.
Talent Trees: Boring and/or highly specialized talents have been removed. Talent points will be awarded roughly 1 point for every 2 levels gained (41 points by level 85). Primary specializations will require a 31 point bonus before allowing any points to be spent in another tree.
Mastery: Automatic passive bonuses will be awarded as soon as a specialization is chosen. These are flat percentage bonuses and are not dependent on the number of points spent.High level items will yield a Mastery stat and Mastery, as a passive skill, can be learned from class trainers at level 75. The stat can further be enhanced by using items with that particular Mastery Rating.