Google Does Not Use Meta Keywords, But Yahoo Does
As stated on Google’s Webmaster Blog at Blogspot, they do not (and have not for a while) used Meta Keywords to impact their algorithmic ranking for web search. They do state that they can use it for enterprise search, but not general web search.
However, don’t go deleting your Meta Keywords just yet. This blog post by Randy Duermyer illustrates a test they did showing that Yahoo does utilize Meta Keywords currently in their algorithmic ranking. When the company doing the website removed the Meta Keywords from a website, the rankings in Yahoo dropped. When the Meta Keywords were restored, the rankings returned. Here is another article describing Yahoo and MSN using Meta Keywords.