Well, most of the classified websites force users to register, flood their with ads and spam. Craigslist don't. When I first moved to NY, I was looking for a new place to live and thank to Craigslist, I got it. Did you know that besides Craigslist, no other websites out there offers you for free? all of them require fee just to see the contact info. A year later I found out that there are tons of other things that I can do, and then I got my first part-time job there in a language school.
I hate Ebay, but can't blame Craigslist because I can see that Craigslist makes no/very little of money right now. Just hope that evil Ebay still keep at least some of good aspects of Craiglist.