I was creating some yahoo search marketing campaigns a few days ago, there was a "did you know" tip in there saying that the advertiser ought to use meta tags.
I haven't seen a recommendation for meta tags since 1998.
Google may use snippets of text from the description meta tag, but I have tested it and a page will NOT rank on Google for a keyword if that keyword is just in the meta description and nowhere else.
On Yahoo, however, pages do rank for keywords found in only the meta description tag.
That jibes with my theory that Yahoo is falling into a slow but inevitable decline to an oblivion hovering somwhere in quality just above Alta Vista. Google keeps leaping ahead on the quality of search while Yahoo rolls out more stuff to sell.