Data visualizations have progressed in almost all craigslist competitors (and mashups), but visualizations won't be the death of craigslist. The battleground is content. Sure there's plenty of spam and scams, but people love craiglist listings because there is so much unique content.

One major contributor to craiglist becoming so successful as a website is essentially the ease of posting content. That lead to lots of content and not coincidentally lots of traffic, but it also means that much of the data is unstructured. Creating more intelligent ways to interact with data requires some structure, but the easiest way to structure data is to complicate the listing creation process. When someone figures out a great balance and has enough search traffic to keep listers coming back, craigslist will have a real competitor.