In a couple of days time, we'll all need to be leveling our characters towards level 80.

Now, for Warlocks the standard school of thought is to level as Demo.

The thing is, I'm not sure I like the new Demo, and (as Wazz provided in Black Temple by beating my behind on the DPS charts) I'm not sure it likes me either.

So, here's an attempt at a Drain Tank levelling build in affliction:
http://www.wowhead.com/?talent=IfxbburhoVVousx0gcz

First thing, I've made an assumption here that you have two pieces of T5, and don't mind wearing them whilst levelling. (Hopefully they should be good up to level 75, and only a minor performance hit until 80.)
The idea is, you go around with a pet in tow; DoT up and drain tank the mobs, and share 20% of the damage you take with the pet - which then gets healed using your T5.

The Imp would be the classic pet to use for this one due to its cloak, but a Felhunter (for the buffs) would be pretty good as well.

You'd probably get most of your mana from Life Tapping, but seeing as we're going that way anyway I've taken Dark Pact as well.

Obviously this build has a slight problem; you need to be level 71 before you can use both Haunt and Soul Link. But, that's easily solved ^_^;;