it's a hard problem in general because craigslist has such market share... when myspace was that dominant back in the day every one knew they would fall eventually because myspace was such a pain to use.

craigslist's problems are not so glaringly functional. They have safety problems with anonymous posters and scamers. They have issues with locking out people in the development community. I've heard a lot of complains about their forums.

It's hard to figure out the best way to attack though problems in a way that draws people from craigslist to a new service.