Stay with a fellow HNer for SXSW
airbnb.com
airbnb.com
I googled a few combinations of the following keywords "airbnb couchsurfing safety precautions screening" (etc.) with no specifics. It looks like airbnb leaves safety entirely up to the participants.
I'm guessing the majority is based on ratings... so you end up with a bit of the chicken and egg scenario... so at first it would seem everyone's gotta take a bit of a risk.
I have met really nice people on CS and have actually dated a few people I met on courchsurfing. I would highly recommend it to everyone.