I like one or two designs, but I can't say that any of them is "better". It's easy for designers to pop Photoshop open and start moving things around to provide a final "web 2.0" layout or a "more beautiful" look and feel, without looking at analytics and studying user behavior. CraigsList is useful, but not very usable. And sometimes a useful product with low usability score is better than a usable product, that 50M existing users need to re-learn. Muscle memory plays an important role for existing customers, especially frequent visitors.

Craigslist is a profitable business. And they need to evolve incrementally the same way Amazon does.

The fact that it's simple and basic doesn't mean that it's broken. It works. At least 95% of the time :)