Matt Cutts, from the Google “Search Quality Team”, officially denies that google uses the meta keywords tag in its algorithm that creates web rank. According to Matt you could leave the meta keywords tag out of your page and it would not make a lick of difference. Even though those are my words and not his that is certainly what he meant.
The video below was posted on the Webmaster Central Blog. According to the article and logic there is no way to overuse or under use a keyword in that tag. Matt Cutts says, “At least for Google we do not use that information in our ranking even the least little bit”. I beleive him.
Check out the video below and check out Google Webmaster Central  Blog.