The Top 10 San Francisco Airbnb hosts collectively control 248 property listings

"The top 10 San Francisco hosts on Airbnb collectively control 248 listings, or 5.2 percent of all the places for rent. They include property managers, hacker hostels and even hotels.
The No. 2 host by listings, Come2SF, with 51 houses and apartments, is also a property management company."

Source:  SF Chronicle, June 2014

Note - The full article has maps, and lots more data about Aribnb in San Francisco