I was in the previous batch @ 500startups and I don't think any of the ~28 companies had a solo founder. Doesn't really answer your question but just an FYI.
Actually I'm fairly sure there were 2 teams with single founders at the time of application. All had a team though, that's the most important thing.
we prefer teams, but we do accept solo founders occasionally... if yer friggin' awesome.
Thomas Korte from Angelpad has said he's accepting solo founders.