Maybe the effect of this will be to make people want personal connections (via fb graph or whatever) to their AirBnB guests, or at least requiring minimum numbers of positive reviews from known sources (to prevent the sockpuppet/shill issue).
I wonder if your renter's or homeowners insurance might cover this kind of thing. If it doesn't generally, it'd be awesome if AirBnB could work with a third party insurer (per jurisdiction) to offer optional insurance to hosts (and guests) against this kind of thing.