Glad to see Airbnb getting some good press. It's really a well-designed service worthy of praise. I stayed in a tipi in a local couple's backyard during a trip to SF last weekend thanks to them. http://www.airbnb.com/rooms/16745
I guess the guy sums it up at the end, that most people are regular people like you and me, but I would be afraid of that one person that is not, or staying with that one person.