@Gary – I base some of my views largely on what Google's own search team have said on this topic: http://googlewebmastercentral.blogspot.com/2008/09/dynamic-urls-vs-static-urls.html

I know that lots of people will argue black and blue how good SEF URLs are for rankings (and that the Google guys are full of it), however most of those people make money from doing such things for other people. I will argue black and blue that the most important things are actual content and a structure that reflects that content, most importantly title tags. Meta tags that reflect actual page content will also quickly push up a site's rankings. Good, descriptive, keyword rich and unique page content is very important.

@Luke – I have never looked at the URL in search results and I doubt very much that many people do. The most important thing is the search result title (which links to the result). Here is where good, dynamic title tags come into play in a huge way. This is the first place I always look in search results and often the only place. I have many times seen search results where each title is just the same static page title for every single page on the website (a standard osCommerce for example).

Looking at the link you posted, the most important thing I have said ranks at number 1 with "66% very high importance" for page specific factors. This is contrasted with SEF URls which is at number 10 with "33% low importance. These figures are of course based on people's opinions, which are more abundant than….