Google Sitemaps has been propagating blogland recently:
By placing a Sitemap-formatted file on your webserver, you enable our crawlers to find out what pages are present and which have recently changed, and to crawl your site accordingly.
For non-web techy folks, that means Google will be able to include your website contents into their search engine more accurately and readily.
A Sitemaps generator for WordPress sites has already been created. I haven’t tried it yet, though looks correct.