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Exciting news. Yahoo and Microsoft have joined Google in support for their sitemaps protocol. The protocol essentially describes a format for files (not visible to users) served specifically to aid the search engines in indexing a site, with the ability to note things like how frequently a given page is likely to change and what url combinations may actually refer to the same page. Some sitemaps tools have always been a part of Google’s handy webmaster tools, but now the protocol has a home all its own.
Sites have grown (and will continue to grow) more complex and while what is usually good for your users is also good for search engines, there are exceptions. The protocol allows the site to explain to search engines what is really important about itself, which can be profoundly helpful. The fact that Yahoo and Microsoft have joined in means a single format, less work and greater impact. It may be time to consider sitemaps files for a wider range of sites.