"In San Francisco, the new measure, dubbed the Airbnb law in tribute to that vacation-rental site’s runaway popularity, came into effect Feb. 1. It allows permanent residents to rent rooms or homes for less than 30 days after they register with the city. Such short-term rentals had long been illegal, but that ban was loosely enforced."

What are our thoughts on this?

It is silly to think that these income entrepreneurs are going to self register. If the cities want to collect hotel taxes, then they'll need to do it through the marketplaces themselves.