"One notable finding is that Airbnb hosts renting out their homes are generating income that is crucial to them staying in the place they live. About 60% of the hosts in the survey had an income less than San Francisco’s median income. About 14% had an annual household income below 14% and another 27% were between $40,000 and $70,000. So for these hosts the extra income is very substantial."
and if there's any doubt remaining, let's ask the head of public policy at AirBnB for her opinion:
"'Hosts really use Airbnb to make ends meet,' says Molly Turner, head of public policy at Airbnb. 'One of the findings that most surprised us is how important Airbnb is to hosts. It’s really helping them through tough times.'"
http://www.forbes.com/sites/tomiogeron/2012/11/09/study-airb...
Seems like we have a problem with rent control there. Many landlords won't rent in SF because of rent control. They want tenants who leave regularly to take advantage of the rising prices. Not sure whether it's cause or effect, but I just think there's clearly more influential factors than Airbnb here.