Google Sitemaps is a good idea — it’s a standard XML format for site maps. Google (and anybody else) can use such a sitemap to get information about site structure without having to crawl the entire site. The sitemap can contain information about the URLs in your site, including how often they are updated and how important they are relative to the other pages in your site.
I generated a sitemap for Semicolon using Google’s sitemap_gen program, an old server log file and a bit of tweaking. Here’s the inaugural Semicolon sitemap. I have submitted it to Google, so I will be interested to see if this has any effect on Google’s indexing of Semicolon.
Presumably Google won’t actually believe what’s in the map, but will only use it as a guide to how to index your site. Otherwise the potential for abuse could be always be there.
It will be interesting to see whether this takes off; I am already planning to write a WordPress plugin for it.
Update (7 June 2005): Dirkz has already written a Google Sitemaps plugin. That was quick! I have been thinking about nice ways of automatically updating the change frequency field for each URL. “Daily” is a reasonable default for the home page, but probably not for any other pages. I think “weekly” or “monthly” would be a better default value for non-home pages for most blogs.