My two experiences:
- roomed with a complete stranger freshman year. Result = complete success.
- roomed with my best friend sophomore year. Result = complete disaster.
- roomed with a complete stranger freshman year. Result = complete success.
- roomed with my best friend sophomore year. Result = complete disaster.
Yeah, I guess the situation is this: What makes a good roommate situation is you don't inconvenience each other. So you have to the same expectations about mess and noise and personal property. I'm going to go without this time.
I think the key to my good experience was that he was always in the library studying. The key to my bad experience was that the guy partied as hard as I did.

That said, it's time to find a new one and I can't really think of any solid indicators of whether we'll be good roommates or not. Most people at least fudge the truth about how much noise they make or whether they're clean or not. Even people who know each other very well, such as best friends, may not get along and part ways as enemies.
What do you guys think?