So after a few attempts to complete the download of 4.01(8GB free space isn't enough fyi)I was able to respec, and get in a few heroics.
Initial thoughts are; Whoa, this feels clunky, weird!, oh that was cool, I need to spend some time learning how to do this all over, why do I feel so squishy, threat doesn't seem to be a problem, picking up adds (like in the gauntlet, in UP) is challenging.
Keep in mind this is WOTLK 4.01 patch, not Cataclysm. Also I think some of this will just smooth out with more familiarity in the new play style.
Admittedly the "clunky" feel, and challenging add pick ups, are most likely side effects of just getting familiar with all the new talents, abilities, procs etc... Given some more play time these should smooth out nicely.
Several heroics later...
Loving the new Blood Boil animation.
Threat seems really good. The only issues I ran into was DPS'ers attacking the wrong targets, and/or attacking the adds before I could get some threat on them. Since those problems are typical of DPS players. I will not worry too much about that for now.
One really good thing I noticed is that my DPS went up considerably. I'm sorry I can't give you any numbers, but first look it appears it's gone up 400-600 points, in these 5-man heroics.
One major thing is that even though my health went up by about 6000k, after spec'ing, and training and getting into tank gear, and turning on blood presence. I feel very squishy. Several times I was asking the healer about that but the replies were all healing is a breeze. So maybe this is just an illusion. I'll see how it looks after a bunch more instances.
Overall I'd say this looks good and should be pretty fun leading up to Cataclysm.
Hint: I heard that DK frost PVP is "pwning" right now so maybe for fun I'll go check that out. This is just what i heard so take that with a grain of salt...
Thanks for reading.