Ah, warlocks. Before the Burning Crusade, there was no class I hated more. Of course, my opinion of the class did a 180 once I got my own Warlock to 70. This build (and variants of it) is often called SL/SL, because it picks up both Siphon Life and Soul Link (talents in the Affliction and Demonology trees, respectively). Unlike most other Warlock builds that focus on damage output, this build is meant to help you outlast your opponents by mitigating some of the damage you take, while using Siphon Life and Drain Life to get your health back. Warlocks with this build can be annoyingly difficult to kill, and is still a popular spec in 2v2 Arena.
The downside (and there's almost always a downside, folks) is that you won't top any DPS charts when it comes to PvE -- it's just the nature of the build. If you think you can live with that, I strongly encourage you to try this build out for yourself. I'm a big fan. And if you're looking for even more info on it, Zach covered this build in-depth last week.