You lost me on the hostel part, but that could be because I'm getting old. :) And the credit card issue isn't that much of a problem since AirBnB handles it and the person you're renting from never sees it.
I considered using AirBnB for a trip I just booked to Greece, but I decided against it. For several reasons:
1. I don't know how clean the place will be. With a 3 or 4 star hotel with good reviews online, I can be fairly certain I'll get a place that is clean.
2. I don't know how secure the place will be. The rooms I booked all have in room safes, so I can leave my netbook in my room and be fairly certain it will be there when I get back.
3. Getting a private apartment on AirBnB isn't that much cheaper than a hotel. No offense to the hosts offering a room in their place or their couch, but when I'm on vacation, I don't want to share a place with people I don't know. I'm just not that type of person.
All of that adds up to general uncertainty over the use of AirBnB. And if a company I was interviewing with wanted me to use AirBnB to find a place to stay, well, that would give me serious reservations as to whether or not I'd want to work there. The possible exception would be if I were interviewing with AirBnB themselves.