I recently did some SEO work for a client, whose web designer later suggested I didn’t know what I was doing because I hadn’t touched the site’s meta keywords. So I went looking for a credible source stating that meta keywords don’t matter. I didn’t have to look hard; a little over a month ago, Google’s Matt Cutts posted this hard-to-misinterpret announcement on the Google Webmaster Central Blog: “Google does not use the meta keyword tag in web ranking“. Matt McGee captures the significance of this post in his Search Engine Land column:

Google is telling the world what every seasoned webmaster and search marketer should already know: The keywords meta tag has no impact whatsoever on how Google’s search engine ranks pages. None. Zilch. Nada. And while Google often needs to be somewhat ambiguous when talking about how it ranks pages, the message in today’s blog post is perfectly clear …

Here’s are some key excerpts from Google’s blog post:

Q: Does Google ever use the “keywords” meta tag in its web search ranking?
A: In a word, no. Google does sell a Google Search Appliance, and that product has the ability to match meta tags, which could include the keywords meta tag. But that’s an enterprise search appliance that is completely separate from our main web search. Our web search (the well-known search at Google.com that hundreds of millions of people use each day) disregards keyword metatags completely. They simply don’t have any effect in our search ranking at present.
Q: Does this mean that Google ignores all meta tags?
A: No, Google does support several other meta tags. This meta tags page documents more info on several meta tags that we do use. For example, we do sometimes use the “description” meta tag as the text for our search results snippets […].  Even though we sometimes use the description meta tag for the snippets we show, we still don’t use the description meta tag in our ranking.
Q: Does this mean that Google will always ignore the keywords meta tag?
A: It’s possible that Google could use this information in the future, but it’s unlikely. Google has ignored the keywords meta tag for years and currently we see no need to change that policy.