Comment by adunsmoor

Even if you go with the "it's not their data" argument Craigslist would seem to own the specific compilation of the data. I'd apply the same copyright principle as phone books or encyclopedias.

http://www.bitlaw.com/copyright/database.html

Craigslist invested in the infrastructure to enter, store, and display this information. They should be able to set their terms as to how it is used in aggregate.