Google Blog: Webmaster-friendly
We’re undertaking an experiment called Google Sitemaps that will either fail miserably, or succeed beyond our wildest dreams, in making the web better for webmasters and users alike. It’s a beta “ecosystem” that may help webmasters with two current challenges: keeping Google informed about all of your new web pages or updates, and increasing the coverage of your web pages in the Google index.
Initially, we plan to use the URL information webmasters supply to further improve the coverage and freshness of our index. Over time that will lead to our doing an even better job of delivering more search results from more websites.