Meta tags are probably one of the most misunderstood components of SEO. Many folks think that if you stuff your meta tags with relevant keywords that it will help your rankings. According to most of the major search engines, meta keywords are not relevant for their algorithms. In the early days of the web, meta keywords were relevant for helping the search engines decipher what a page was about. However, this set up was rife for abuse. A webmaster could “stuff” the keyword meta tags for certain keywords and achieve some level of significance. Nowadays (2009) it is much more important to have good content, and relevant links.
If you are going to use meta keywords it is important that they are completely relevant to the content on your page. But many well known SEOs do not even use meta keywords anymore.