When I went from html pages to php/mysql is when my
seo actually went into high gear. Using a db, you have the option of creating huge, category killer sites. My one tip is to learn mod rewrite. Despite the fact that Google says that they crawl dynamic pages, dynamic sites seem to be put on the back burner. I actually have a site where I left one part of it purely dynamic and used mod rewrite on the rest. The page that still has the dynamic url has no pagerank after the last pagerank update, while the rest of the pages on the site have pagerank assigned.