How much does Google use the keyword meta tag? Not at all according to a post today on the Webmaster Central Blog.
Does that comes as a surprise to you? For many it won't but it's always nice to have some verification and today it came in the form of a video from Matt Cutts, Google's Head of Webspam. Google does (or will) use the meta description tag occasionally as a snippet for the description which appears in the search results, but it is important to note that Google does not use the description meta tag in how it ranks sites.
A rather insightful comment was posted by Michael Martinez on the post who said it would be helpful to Webmaster if Google used it in their Custom Search Engine solution and/or site-specific searches. We agree completely. The keyword meta tag is used by the Google search appliance but it does not influence organic results at google.com.
So should you leave the keywords meta tag empty or not include it at all? According to a some respondents on the post, some search engines (Yahoo! and Ask) still do use the keyword meta tag. Keeping it might offer some "insurance" just in case some engines do factor the keyword tag into their algorithm.