Nice post, this is pretty much what I've gone for as well.
A couple of points I'd like to add.
Elitist Jerks recommend that for multiple targets Death & Decay is added after the application of the diseases along with adding Blood Boil and Icy Touch instead of Festering Strike. Not sure I can see the value of another application of IT though, but they obviously know better than me
I always liked the idea of adding Anti Magic Zone as a raid utility in the cases of heavy magic targets. However as no one has suggested taking it I assume that the extra dps and mitigation from other talents is better.
One other point I've noticed is that the wonderful Dark Transformation is pretty much a waste in solo play at level 80 as I've never got to 5 charges of Shadow Infusion before the mob goes down. It works in HC dungeons but I've never tried the new spec out in raids. Presumably it may come into its own with the harder hitting mobs in Cata.