At Search Engine Land, Barry writes about how a US court has decided that META keywords don't matter -- they are "immaterial." The tip came from Eric Goldman's blog where he writes about a recent case that held a company responsible for including trademarked terms in their meta tags.
In this case, because search engines don't use the actual META tags, there is no case. Jill Whalen says on Sphinn that you can test this easily by including a page with an arbitrary word and seeing if that word will come up in your search results once Google spiders the page.
META keywords are not discussed in this Google Help document which should support the law's findings.
However, as another member points out, Yahoo may be using these keywords to rank. In other words, the US Court is overly focused on Google, but perhaps they should weigh in on other search engines.
Forum discussion continues at Sphinn.