Blood tank with 3 frosties is a fast and easy way to clear instances. I use that 80% of the time or more clearing the level 85 5 mans and heroics. I run a pally healer and 4 DK's. For tougher fights i spec all 4 DK's blood but only one is the tank in blood presence. The other 3 are in unholy presence and rocking the new Death Strike glyph (glyph of Dark Succor).

Yeah the dps isn't the greatest but the massive heals they produce make some of the harder pulls/bosses doable. With the glyph they heal themselves for around 18k as well as getting the blood shield.

I generally drive the team using my Holy pally but i also run the 4 DK's with healer friends and have had some success doing 5 man stuff that way.

Good luck and i hope you keep enjoying the DK's as much as i have been!