Hmm, I'd heard about that site but never tried it and didn't think of it.

I very very strongly prefer either someone I know (and at whose place I can leave some of my stuff during the day), or someone attending the same conference. If I can't find either of those but come up with something else... I'll be ambivalent. Trying to effectively attend a conference while staying with a stranger who isn't attending it sounds troublesome - might work out well, might not.