Most of the loc fields in my sitemap are using relative URLs, for example:
<loc>/blog/index.php/2006/12/19/all-hail-to-the-january-effect/</loc>
According to the sitemap.org protocol, this is not allowed. "This URL must begin with the protocol (such as http)..."
It looks like all of the post URLs are relative but the pages and misc links are absolute.
http://wordpress.org/extend/plugins/google-sitemap-generator/