I'm using Google Sitemaps on three of my web sites and to be honest I am disappointed. They have been running for 2 months and verified since day one and the sitemap files downloaded on all three web sites humerus times/
At the moment Google still don't list any knowledge of two of the sites, even though they have downloaded the sitemap files. If you read the Google Sitemap Discussion pages, you will find that I am not alone with this problem.
Other people have seen their sites vanish from Google listings from a high page rank to nothing since using Sitemaps.
I get a higher ranking from Yahoo! and MSN through normal bot crawling than I do for Google sitemaps.
Another huge security flaw with sitemaps was the verification errors, which have now been fixed.
To get stats for your site you have to upload a file with a unique file name Google give you to you server, you then ask Google Sitemaps to verify this site exists and when it does you get access to stats.
However a number of Servers, including Google's, AOL's, Amazons etc servers didn't respond with the correct 'File not found' error when asked and responded by either auto generating a file name it was being asked for and displaying a custom Not Found page, therefore the Google verification assumed the file did exist and you could look at stats for other web pages.
More info here:
http://www.davidnaylor.co.uk/archive...ogle-sitemaps/