Larsen-
How gear dependent is your build, would you say? You made me a believer in your build so I leveled with it. However, I thought it was really lacking with my gear (no spell power). DP costs a GCD and restores ~160 mana when you get it (150 base plus SM bonus), and that is way too little. Each cast barely covers each DoT's mana cost. When mobs are spread apart it's fine because I have time to spend GCDs on DP while running, but in all other cases I'm spending so many GCDs recovering mana and not dealing damage.
Another thing, wands are better than Drain Life for DPS until 38+. Before then I don't see the value in even using Drain Life, let alone Drain Tanking and spending 10 talent points buffing DL when you can wand instead for MORE dmg and more resources (via spirit regen). Drain tanking is also underwhelming without spell power, since you lose so much efficiency when you take damage. Even in the 40s and 50s, I found that using Fear was more valuable for efficiency if it saved me 2-3 hits, and using 175 mana to cast a spell that does no dmg didn't feel good either.
FWIW, I plan on leveling another warlock and this time I will be going Imp VW+Imp DS until at least 40 something when I can have some Shadoweave pieces to complement Drain Tanking and support DP. It makes sense on paper that you should dump your VW once he can't keep threat from you.
