Matt Cutts of Google presents this video to officially and formally end the conversation over the efficacy of the keywords meta tag.
If there is any doubt in your mind, please allow me to make it explicitly clear …Google has never considered the keywords meta tag in their algorithm. Don’t waste your time or energy or create a false sense of security by going through the effort and the motions of creating keyword meta tags. They are completely, 100% irrelevant to being found on Google. After all, the whole point is to get found on Google.