goodroi - 8:40 pm on Nov 1, 2012 (gmt 0)
Sitemaps are a magic potion that can significantly boost rankings for websites that Google can not crawl. For the other 99% of the websites that exist sitemaps are not critical and have minimal if any impact on rankings. Google prefers finding your pages via links not sitemaps. So make sure your pages are linked.
Google also disregards much of the information they are told because many inexperienced webmasters forget to change the settings when they copy one of the generic sitemap files. Google prefers to determine themselves just how often you are changing the pages instead of relying on the honesty and accuracy of webmasters.