That friend in Illinois was very uncomfortable with the idea of sleeping in some random person's house, and I didn't realize how absurd it sounded until I was listening to myself explain it to him and his very uncertain reaction. The reputation/trust element removes that "randomness." So much so that I won't book with listings that don't have any reviews, and I tell my friends the same thing.
Personally, I think the "weird factor" around AirBNB will probably be harder to erode than the one around online dating. I think the existing hotel industry comes a lot closer to meeting a wide range of people's needs for accommodations than the standard informal "go out to a bar or meet people through mutual friends" thing does, and for someone like me, who travels fairly infrequently, I don't mind spending more once or twice a year to have that extra identity/trust from the known quantity of an actual hotel.
[1]"A lot of people were initially hesitant (and still are)"