If you think about it, there are billions of people in the world, all of whom have different personalities and values. Having a roommate picked out of a hat means that you'll get one of these people, and who they are is up to chance. Because of this, it's often up to chance whether they're a perfect match or a complete flop, or somewhere in between. If you're willing to take that risk, be prepared to discuss with your roommate lifestyles, bed times, noise levels, etc., so whether or not you rub along, you'll at least have clearly defined rules that should make your experience easier.
For me personally, I bunked with a close friend of mine, and we hang out all the time. Just last night, we went as two 'Creepers' from this video:
http://www.youtube.com/watch?v=tLPZmPaH ... ure=relmfu for Halloween. I got completely piss drunk and now I feel sick.
Good luck!