Patch 4.0.3 and the Cataclysm expansion are approaching quickly, and frankly, we're in pretty good shape right now. Yes, there are issues you can point at in almost every tree that could be just a little better, but honestly, most of them are pretty minor. We're really solidly set up for leveling (if you don't mind leveling in a tank spec), dungeon running, and even the first tier of raiding, and for now we can feel pretty secure about ourselves (or at least about our class).
That said, there are almost always improvements to be made, and I do want to take a little bit of time to talk about the issue of the unholy tree's complicated love-hate relationship with haste. Now, you're still going to be stacking and gemming strength as much as possible when you gear up. Strength is still king, don't get me wrong, and you'll always want to get your melee hit capped out. But after that, haste pretty much rules for the roost for unholy. It vaults past critical strike rating and leaves mastery somewhere two or three miles down the road, it's so good.
This isn't too much of a problem at first glance. It's arguably a little boring stacking one secondary stat over others, but that's more or less a reality of gearing up a DPS. It's very rare that two secondary stats share equal billing. We did have a problem with reaching the GCD cap early on in the beta, but the addition of a GCD reduction element to Unholy Presence fixed that pretty handily.
That said, there's still two big problems, one of which primarily affects unholy, the other of which affects all three trees.