Going to slightly necro this thread, as I saw it mentioned by dilbrt, and as he's the person whose posts have made the most sense to me regarding DK's, I'd like his opinion on this spec for tanking (anyone else should [and will, I have no doubt] feel free to comment):
14/50/7 I've not had a chance to use this in a group yet, just for an hour or so in Icecrown.
I'd say the main reason I wanted to try this is because I liked the idea that some the rune abilities I use the most (Pest, BS, DS and OB) would all turn into Death Runes, but like I say I've not had the chance yet to see if this actually benefits me at all.
One thing I did notice this morning when I respecced was that I seemed to have 3 Death Runes permanently, as in not even in combat, but I was fairly tired then, maintenance is on now and I just finished work (3am here), so I could be missing something obvious.
I know I would only need 13 in Blood to max out DRM, but I couldn't see any much better places to put the extra point, so 4/5 Bladed Armour seemed as good a place as any, and it does give me ~450AP.