Interesting. Google is introducing specifications and protocol for a web site map. This will be an XML document containing links of your site, their modification date and frequency of change. The goal, with no guaranty that this will be done, is to improve Google's crawling and indexing your site (and supplements Googlebot's usual crawl-based mechanisms)
Such a site map is easily doable for database driven websites such as blogs. I expect some activity in the WordPress community on this topic in the next days, and a quick user has already written a first Google Sitemap Generator for WordPress. This is a nice start, and I have commented the page with some suggestions to improve it.
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