Google, Yahoo! and Microsoft have collaborated for the greater good and are all going to support a standardised XML sitemap protocol.
Google was the first to implement the XML sitemaps in June 2005 as a beta product. After a few months of public testing, the beta tag was removed and the service was ready for general consumption. Since that time, Google Sitemaps gained a significant amount of momentum.
Its wonderful to see that Yahoo! and Microsoft didn’t implement another format specific to their own search engines and have collaborated with Google. With the standardised XML format, its now possible for content publishers to feed Google, Yahoo! and Microsoft search engines off the same physical file. That point alone is a huge bonus for the publishing community though I think even more significant is that the standardised format will have the same semantic meaning to all search engines as well.