My experiences with WS have so far been positive, but there is always the possibility of an unpleasant or incompatible guest coming to stay which may make for an awkward stay. I've also hosted people from Couchsurfing, and the experiences there have been more negative than positive, so I am far more selective in allowing people to stay from CS.
Do you do anything to try and ensure that potential guests will work out? Is it appropriate to ask that they provide you with interesting stories from the road? (Because this is the only thing that I really want from them.) Entertain me!