Ok so healers that I party with (both guildies and non) are saying that I get hit like a truck in Heroics and in ICC.
Now when ICC his I tanked the first wing but found out I was stressing the healers out because I was taking so much spike damage. So I have since switched to DPS so I can have a spot in the raid. I would rather tank but people on my server are saying DK tanks are a bit broken right now.
I can't offer any tanking advice but I can tell you for a fact that I hate healing blood DK's. When they get hit, they get hit really hard and I usually have to spam heal them through the "easiest" of heroics. I think it might have something to do with the fact that they are not using their healing abilities as they should. But then again I don't know that much about DK tanking.
It might not be just you, but how all Blood DK tanks opperate. They are "squishier" then others tanks if I understand correctly.