I've fooled around with the Blood and Unholy specs and I'm definitely going Unholy spec when Wrath hits. It's so much more fun than Blood in my view. Having a permanent pet ghoul, desecrating the land and exploding corpses is too much fun to turn down for some blood worms and health regen. I'll probably level my Death Knight to 80 someday but I probably won't do any raiding on him. Frost might be fun but I haven't tried it.
On another note, there's been some pre-expansion guild drama and we had some class leaders and some dps leave the guild to start a new more hardcore guild on another realm. Losing the rogue class leader really hurt as he was a great person and contributed a lot but good luck to them anyway! I think we have a solid core of raiders and that will attract new talented players when we start to raid at 80. I guess though that this drama sort of put an end to our Sunwell progress so we will have to settle for having done Kalecgos. Most of us felt that Illidan was the real boss of BC. He was our goal to beat when the guild formed and back then we never thought we'd actually reach him. I did feel content when I downed him for the first time. Sunwell was great and I would have loved to seen all of it but it wasn't meant to be it seems.
This is our first expansion drama/change which we have to deal with as a guild as we weren't formed when BC arrived. I'm certain we have enough structure and routine to be off to a good start at 80 though.