Points off, Craigslist, for changing the urls of something people have bookmarked and subscribed to without any kind of notice or even notification. But bonus points for for choosing a better url for things artistic. I can only think you changed urls because you found that people were “guessing” the url “/art/” and getting confused. URLs are user interface.
If you look at Google right now for this search, you can see Google still thinks the old url applies. It’ll catch up soon I bet.
Given that Craig Newmark is a web guy, I always looked at the /art/ url as a kind of nod to the “artistic” aspect of making web pages. A tiny appreciation of HTML geeks like me. I suppose that’s a bit of wishful thinking on my part.