I noticed that Craigslist recently introduced a series of buttons at the top of their listings. These buttons are designed to assist in the moderation of posts, so the staff of Craigslist doesn’t have to. Included in the group are implementations for miscategorization, prohibited posts, links to discussion boards, voting for “best of”, as well as marking posts as spam.
I assume the spam button utilizes IP address information to prevent posters from voting listings competitive to theirs off the site, but you can never be sure. Even if it does, I expect there will be a lot of abuse in this regard before the site gets it right.
Personally, I would not have opened the site up to this type of community involvement. Everyone knows Craigslist is a free source of PR, which means it is ripe for gaming, much like Google has turned out.
It is going to be a constant fight to keep the sleeze from working this implementation to their advantage. The trouble it could cause the staff at Craigslist may turn out to be more of a burden than the alternative, which is to use some of the (purportedly substantial) dollars the site is taking in from job classifieds and investors, for a more rigorous anti-spam agenda.