So tonight I took the plunge and tried 2v2 random with my friend James.
Game 1 I got protoss (James plays protoss as well) and we didn't wall in and died to mass lings. No problem, only the first placement match after all.
Second game I spawned terran and we were vs a toss/terran team as well. We died cause they know how to make units faster. Again... no problem :)
Third game was finally a win! I spawned protoss and we were able to overwell our zerg/protoss enemies. The first attack looked grim (and I tried to get VR's which didn't work against the opponents stalkers), but after that I focused on macro and making units from my 7 gateways which ended up working out ok!
Last game I did spawn as zerg but we were against two zerg. One tech'd to ultras (which we just let him do, stupid us) while the other just got roach hydra. It didn't work out in our favor when we finally attacked since we had a ground army (him stalkers, me lings/roaches).
Definitely learned some things and had fun playing random!
Here are some screenshots from the game we won: