As my sig suggests, my first team to 80 was a 4 class mixed group - Pally, 2xMage, Warlock, Priest. After the new Dungeon Finder launched I took the opportunity to rapidly gear my tank ... and for the first time actually played each of the dungeons from the solo point of view. One thing I noticed was how everyone used AoE on the trash instead of CC. Big difference. So, I went and solo'd my warlock through a bunch of instances. Horrible gear (avg ilvl was around 180). However, I managed to go from 800 DPS (you've read that correctly) to >2200 DPS (same gear) simply with a respec and a change of rotations (yeah forum search!)

Now that I understand a lot more about warlocks, I decided to level a team of them (if 1 is good... 3 is better, right?). SoC in heroic trash clearing is simply epic... x3 and it just seems like it will make my runs smooth and fast.

My new team consists of my old main Pally (who was left at level 70 when I started mBoxing), 3 Warlocks, and a Shammy healer. Last night I hit 68 on my slaves, and tried The Black Morass. With my old team, I was never able to do it until I leveled to 80 and went back for the achieve. Here I was, not even 70 on 4 of my toons and trying it ... and cleared the place in record time. No deaths, no issues. The work was mostly done by my FelGuards, which got me thinking... the best of both worlds:
http://www.wowhead.com/?talent#IcxrM...usxzZVo:oq00zV

This build gets a lock the Felguard, 5% more crit on SoC, 5% more damage on SoC, 24sec Immolates (so you can spam Incinerate for just about the whole fight). The Glyphs give the Felguard a nice DPS boost and your Immolate and Incinerate spells a nice DPS boost as well. 1 lock casts CoE, the others use CoA, and you're off to the races.

The true beauty of this is when you have 3 felguards running in mopping things up while I AoE. It has simply amazed me how useful having several pets is. Sure they die... but they aren't there for protection they are there to provide CC in the middle of all the AoE madness that's going on. Oh, and all that free healing they get from the damage the locks are doing? Yeah, it makes them that much more survivable.

For leveling and questing ... I never have to stop. I simply toss CoA, Corruption and target the next mob. The felguards finish them off for me. I can clear an area faster than my mages could AoE because I don't have to "gather" mobs.

TLDR: Try out a bunch of Locks. They are certainly more fun than I thought they would be. My only complaint (and this is a small one) is they don't provide the ports that my mages did. With the new dungeon system, however, that's really not the issue it used to be. Food/Water? I just create it on my mages and hand it out