I'm considering switching my main tank spec from frost to blood. From what I've read, heard it should offer more survivability with some reduction in AOE threat. The other reason is, that's where the tank tree is going anyway in cataclysm so I figure might as well get used to the rotations and gear up a good 2H. Any opinions? Is it worth it? My role is ot in 10/25 icc.
Don't switch to Blood because it will be the tanking tree in Cataclysm. There is a good possibility that DK tanking in Cataclysm will be substantially different than Blood tanking now. Looking for a good 2H weapon as you clear ICC is good prep work for Cata.
If you are happy and performing well with Frost, you don't need to swap over to Blood. Frost is fine for normal 10/25 ICC OT. If you are progression raiding (heroic ICC), then it depends on what you OT. If you're the 3rd tank, then frost should be fine. If you are the 2nd tank or MT, Blood is better for progression raids. Other than Festergut 3rd inhale, Blood has more net survivability than Frost.
Blood is great for single-target boss tanking, a pita for AoE tanking. Frost is great for AoE tanking, and good for single-target boss tanking. Like Miste said, it doesn't matter which you use for regular 10/25s. I actually run dual-spec'd both Blood and Frost and switch depending on the fight.
It might be worth getting a little accustomed to Blood b/f Cata. Some things will change, some will stay the same. For example, learning to time your Death Strikes so their heals aren't overheals without pausing threat gen will probably remain a useful skill in Cata, but the exact rotation will differ.
If Blizz holds true to their stated desire regarding the relationship between health, healing and incoming damage, then timing your DS in Cata will be unnecessary. The massive reduction in overhealing and Blizzard's desire to have tanks below 100% normally will nearly eliminate DS overhealing.
Cata is changing DK tanks. Elements of all three tanking specs will be part of the new DK tanking tree. I expect certain gameplay elements like the frantic spending of death runes will go away with the new rune system and general spec changes. It's almost like we have to relearn our class in the next xpac.