On Monday, Google engineer Matt Cutts posted a video on his blog in which he discussed Google's official policy on meta keyword tags. In a nutshell, they don't use them.
That's old news to SEO firms that optimize web sites to perform on Google. We've known that for a long time.
But, we still have conversations with prospects and clients who ask us to quote an SEO project that entails "updating our meta keywords." In their eyes, updating the keywords tag is a quick and inexpensive fix. The problem is, it doesn't work.
Google gives no weight to the meta keywords tag at all. What they do look at is the title tag, description tag (for purposes of displaying your listing), your content and incoming links.
That doesn't mean that keywords have become obsolete. It's an issue of how you use them. Read my article on The Difference Between Meta Keyword Tags and Keywords.