In 1998, when Google came into existence, other search engines like Infoseek and Altavista were indexing sites using the keywords meta tag. But, keyword meta tag, being a webmaster controlled parameter, can be easily manipulated to stuff it up with irrelevant and undesirable keywords.
While not giving any advantage to keyword stuffing, Google came up with the idea of using external links to rank the websites. Webmasters, having the older conception in mind, believed that Google too uses the keyword meta tag.
Thus, since its inception, Google had never used the keyword meta tag, since people started to stuff it up with keywords even irrelevant to their website. Other search engines might use it but Google, which is the major source of traffic for websites, don’t bother about it.
Finally, after lots of confusions and contradictions, Google officially announced on their webmaster blog that they DO NOT use keyword or keywords meta tag for ranking in search results. Although this is an earlier known fact, but most of the SEOs didn’t believed it and they had the misconception that keyword tag plays a major role in getting higher rankings. It doesn’t solve any purpose other than helping your competitors to steal the keywords which you had chosen after putting in lots of time and efforts.
Google definitely use other meta tags, such as description tag, which is displayed in search results, if it is informative. So next time if some one uses your brand name in his keywords tag, don’t bother to sue him. It’s not going to benefit him or harm you in any way.