How often does Google use the keyword meta tag in the main search engine results and ranking? Matt Cutts says "not at all," and in a video explains why. Even today if one company sues another company, some courts mistakenly believe Google relies on meta tags in the main search query.
That's not to say that Google doesn't use any meta tags. It does for the Google search appliance, which supports site search, so you can specify only return results if they match a meta tag. The Mountain View, Calif., search engine will also use part of the meta description of the meta tag in the snippet.