Sitemaps are an essential requirement for any website. SEO experts recommend that sitemaps help in better indexing of all pages of your site or blog and which helps to drive search engine traffic to your site more effectively. Sitemaps are more important for blogs, because their content is constantly changing and sitemaps help notify search engines about what is changing.
One of my favorite wordpress plugins is the Google Sitemaps WordPress Plugin that automatically generates a sitemap for my site, refreshes it and pings Google. I have been smoothly running the publicly released 2.7 version.
Recently Yahoo, Google and Microsoft joined hands to support a single format for Sitemaps. A Sitemap is an XML file that lists URLs for a site along with additional metadata about each URL so that search engines can more intelligently crawl the site. Sitemap 0.90 is now offered under the terms of the Attribution-ShareAlike Creative Commons License and Google, Yahoo!, and Microsoft will continue to collaborate on the protocol and publish enhancements on the jointly-maintained site at sitemaps.org.
The plugin author has updated the xml-namespace definitions in the new beta version of the XML-Sitemap Generator for WordPress Plugin as per the new sitemaps.org standard. Which means you need to get the latest 3.0 beta 4 version to get these new features. Beta means it is still under testing and has some buggy risks, but beta 4 seems safe enough for me and maybe the 3.0 final release may be out soon (but still try at your own risk). Get the updated version and help Google, Yahoo!, and MSN index your site better.
The best way to submit your sitemap to Google is via the Google Webmaster tools and to Yahoo is via the Yahoo Site Explorer.