I ran a system that was a back end for craigslist for many years, and I never stopped even after getting a cease and desist from them. What really got me was after they started charging people to post ads... that really killed my business model. Generally its not a great idea to build a business model around the availability of a third party... I think the whole concept of craigslist sending a 'cease and desist' over what is generally considered public_html is a laughable joke in my opinion, and good luck trying to restrict public html from crawlers and robots.