Sitemaps are now autodiscovered by major search engines

Ever since Yahoo joined forces with Google and Microsoft in creating sitemaps.org, they have been pondering a way to autodetect sitemaps without having the webcrawlers crawl everywhere to find it.
Now they’ve come up with a brilliant solution. Add to you robots.txt file:
Sitemap: http://www.example.com/sitemap.xml
Where example.com is your URL. This way, all search engines are using a universal standard and will be able to crawl more efficiently and update your sites in the search engines more quickly.
Via YahooSearch