BestEast
SEO services did a series tests that show
1. keywords in URL are taken into account by Google, MSN (beta), Yahoo! and Exalted algorithms.
2. This test does not show how much it helps for your ranking compared to other criteria. When constructing URL directory and URL file names, use targeted and relevant keywords.
3. If you use several keywords in your URLs, use hyphens as dividers and not underscores.
4. while Ask Jeeves, Lycos, Teoma, WiseNut, Voila does not have same result to use keywords in URL.