Google may ignore the keywords meta tag, currently at least -- but Google is not the entire web. Yahoo does use the keywords tag, and some directories do as well.
If it holds a reasonably concise list of keywords that are specific to the page, then I think it has its place. A well constructed keyword meta tag does not look spammy.
I continue to use the meta keywords tag and I advise my clients to. The idea is to keep the keyword list relatively short - a kind of memo for the most important handful of terms that this specific page is focused on. Listing sitewide keywords on every page, however, is a waste of bandwidth.
it's also got some uses other than helping search engines. if you've got your own search facility set up on your site, for example, then you can weight the keywords a lot more than a search engine would (because you'd know whether or not they were accurate). they might also help other spiders, like the adsense one. because that probably weights onpage factors a bit higher than googlebot does.