Big Bear Butt has a good post talking about the changes coming for Crowd Control in 4.2.
Basically, sheeping a mob in a pack will no longer pull the rest of the pack.
I completely agree with BBB that this is a good change. It makes CC much more user-friendly, as it separates the CC phase from the actual pull. Rather than painstakingly marking the entire pack, we will be able to CC first, see that it was done correctly, and then pull the remaining mobs.
The DPS can even CC ahead of time, confident that they won't be pulling before the tank is ready.
As well, it will make tanking easier. The CC'd mobs will stay where they started, while the remaining mobs will be pulled to the tank. This makes it a lot easier for the tank to use AoE abilities without breaking Crowd Control. Essentially, we get some of the Wrath-style AoE capability, while still using Crowd Control.
All in all, this will be a good change for the game.