There was a nice post today on Search Engine Roundtable that showed the results of some testing on Google sitemaps. According to the post, JohnMu of Google noted that Google looks at page priorities in XML sitemaps on a site level and not on an individual sitemap level. This is important because several websites employ multiple XML sitemaps. It is important for those folks to realize that Google takes one holistic view of all the files for the domain and prioritizes them together.