I have been doing extreme testing of this plugin and found many things that are unique to its functionality and use. WP 3.1.1 and WP 3.1.2
Plugin Version 126.96.36.199 and a few previous versions.
First and foremost I found that when I activate the plugin and address the domain http://somedomain.com/sitemap.xml the sitemap is created for the site but when more posts or pages are added they are not added to the sitemap.
However, if I delete the sitemap files (2 - the regular file and the GZ file) deactivate the plugin and then re-activate it - then addressing the sitemap URL the new posts and/or pages are added to the newly created sitemap.xml but only to a certain limit.
On one site in particular there are over 100,000 posts but the sitemap shows only a little over 6000 with tags and categories and 984 without tags and categories.
At this point other then missing tens of thousands of posts - it is a great plugin.
I wish it went all the way though of course :slight_smile: