According to Google’s Matt Cutts, there are better things to spend your time on than stuffing keywords into URLs. Cutts believes the practice–strongly recommended by some SEO experts–contributes little in terms of a site’s SEO performance but can be valuable as a tool to improve user experience.
Cutts believes that URLs containing relevant keywords helps a user decide if the page is appropriate to their needs. Of course, a pretty URL is worthless if not supported by a relevant, informative snippet and a TITLE tag that clearly indicates what the page is all about.