Bah. Just because improve a web site is hard doesn't mean that you don't have a responsibility to your users to TRY. Craigslist has not. There are ways to experiment in a low-impact way. Hell, they could offer a "plugin" system, so that users could add the padmapper plugin.

People keep building things using Craigslist data that users LOVE and Craigslist keeps shutting them down.

Craigslist is one of the great squandered opportunities for awesomeness on the internet.