How many US cities/states/landlords no longer allow their properties to be used for Airbnb?
A fair number, but this often doesn't stop people from ignoring this rule, listing their properties under hidden addresses etc. I would say 90%+ of the AirBnBs I've stayed at are in buildings that have banned them (especially in large cities, like Toronto)
That sounds like a pretty bad foundation for a business model to me.