Personally, I would never pimp out my own home to strangers while I'm away. It seems creepy. Also, inviting complete stangers to stay overnight in the guest bedroom in exchange for a couple hundred dollars (or less) doesn't sound appealing either. There are too many idiots out there, and I'm choosy about whom I share my personal space with. It would take a special type of person to do that.
It can see that it could sound creepy but the reality is quite different in my experience.
I've no experience of renting a place while someone was away so I can't speak for that but I can say that the people who rents out the spare room on AirBnB tend to be gregarious and outgoing. They're the kind of people who like to meet complete strangers. I've never been on the other end of the deal but I imagine the same can be said of the kind of traveller that uses the service.
For me, AirBnB isn't about saving money, it's about a social experience. Of course, if you're a very private sort of person that may not be attractive. But I do think it'd still stop short of creepy.