Craigslist, the internet's dominant source of online classified ads, made news in June when it sent a cease-and-desist letter to PadMapper — a popular apartment-finding service that combines Craigslist's publicly-searchable ads with Google Map data. Since then, the company has changed its Terms of Use twice; asserting, then denying, ownership of its users' posts. It is now suing both PadMapper and 3Taps, which provides the API for tapping into Craigslist's ads, charging them with copyright infringement. 3Taps is fighting the charges with a counterclaim that alleges Craigslist is using is using its monopoly power to squeeze new entrants out of the market.

The question remains whether Craigslist, which does not claim an exclusive license to its users' posts, has the necessary legal standing to prevent other services from tapping into its ads. Is Craigslist using its monopoly in classified ads to stifle innovation in the markets it dominates? Or are 3Taps and others merely piggybacking off of Craigslist's success?