Response from Jim Buckmaster, CTO of Craigslist:

Just every way our users have been able to think of to do the heavy listing, whether it’s the flagging system where users take responsibility to monitoring the site, right down to our business model from the get go, whether we should raise financing or having a sales force of if we should do marketing, if we should charge for anything and what we should charge. So our users have really kept us out of trouble,. Our site is kind of the net result of users suggestions.