Usability 
A person to person service for finding vacation apartments and homes around the world. Property owners post listings of available rentals. Travelers can view listings by date, location and price and contact hosts and make deposits by credit card or PayPal. The site also has user reviews of listed rentals.
I'm a little disappointed by Airnb's mobile site which is limited to messaging between hosts and travelers. Registration, placing a listing, searching for a rentals and making reservations all require using the desktop site.