Plus there needs to be a certain level of creative expression for copyright to apply, so even the sentence, "I have a room in a 2-bedroom apartment for rent in Williamsburg, going for $1500," would almost certainly not be copyrightable. (That said, some of the posts on craigslist are certainly creative, so copying the full contents of everything would likely violate copyrights, but as you say, that's not what Padmapper is doing. (Not to mention the copyrights on the individual posts belong to the users, not to craigslist, in any case.))