One thing I would love to see craigslist do is learn what kind of things I am interested in, so that it could more readily display me ads from people who might have something I'm looking for.

It's great that its so expansive, and search is ok - but sometimes while scouring it, you come up with little gems that make you go "oh wow"...

If you could create something that would give you more "oh wow" moments, I think you'd have enough of a disruptive technology to draw away some of their users.