I have a lot of experience with Google, and especially Google Sitemaps. One of my biggest ones is DO NOT add it to old pages. Especially ones that are doing well - like the say, dont fix something thats not broken! It works great with new sites though, getting them indexed. I suggest using http://www.xml-sitemaps.com to create your sitemap. Make sure the index page is 1.0 priority and the other ones are all .5. Updated Daily. Just my two cents
Thanks for the suggestion, but Google doesn't necessarily follow the priority rules. I use a WordPress plugin to generate mine.
Unless you pay, http://www.xml-sitemaps.com is a toy that generate 500 links sitemaps. It is however reliable and fast, but lacks changing detailed parameters before generating the xml files. A preview should help, not only to see your broken links, but also to change individual parameters, like priority or last change date. I've tryed to make my own sitemap generator in order to compensate these limited and global parameterizing sitemaps. Take a look at http://www.webrickco.com/buildsitemap.php. It will first generate a preview of your links, show what is broken and for which reason, and you will be able to individually change the parameters for each link. Then you will be able to generate your definitive sitemap, according to your definitions. It is limited to 10000 links. Just try it, and give me your feedback on it. Thank you.