DaveN, a man who’s blog I really admire has a post on why not to use sitemaps. To be honest, I agree with him. Build an accessible site with good internal links and you won’t need one. Build a site with poor internal linking and rely on a sitemap and Google will see the pages as having little worth and probably chuck em in the supplementals. If you can’t be arsed to link your pages together properly on your site, why should a search engine bother giving any credence to the content of those pages.