SEO-friendly URLs are all the rage these days. But do they actually have a meaningful impact on a page's ranking in Google and other search engines? If so, why? If not, why not?

(Note that I would absolutely agree that SEO-friendly URLs are nicer to use for human beings. My question is whether they actually make a difference to the ranking algorithms.)

Update: As it turns out, the Google post that endorphine points to here has caused tremendous confusion in the SEO community. For a sampling of the discussion, see here, here, and here. Part of the problem is that the Google post is addressing the worst case where URL rewriting is done poorly and so you'd be better off sticking with a dynamic URL rather than a mangled static "SEO-friendly" URL.

There's no question dynamic URLs can be crawled by Google and can achieve high rankings. Maybe it would be easier to reframe the question more concretely: given 2 otherwise equivalent pages, which will rank higher for the search "do seo friendly urls really affect page ranking"?

A) http://stackoverflow.com/questions/505793/do-seo-friendly-urls-really-affect-a-pages-ranking

or

B) http://stackoverflow.com?question=505793 (a fake URL for comparison only)