I heard these were out a few days ago, but the link I got was to the official forums, and the thread had been deleted by the time I got there. Well, MMO-Champion has them now. Delete that, Blizz! Now keep in mind, as MMO-Champion warns us, these aren't "official" bonuses, but were rather extracted from the currently game files somehow, and will most likely change when 2.1.0 goes live (which according to Tseric will be "soon"). Still, this should be something to get your mind going.
The bonuses mostly follow the same pattern: 2-piece bonuses makes a skill cheaper (or sometimes return more mana), and 4-piece bonuses makes a skill stronger. Since the 4-piece bonuses mostly affect our "bread and butter" skills (e.g. Greater Heal for healing priests, Fireball, Frostbolt, and Arcane Missiles for mages) and mostly by about 5%, they seem pretty cool. The 2-pieces vary in how much they impress me. Tier 6, if I'm not very much mistaken, drops in
Mount Hyjal the Black Temple [thanks, klink-o], which is certainly out of the reach of most guilds, but I'm sure some of us will see it eventually. Without further ado, all the Tier 6 names and (provisional) bonuses are after the cut.