As with most search engine optimization queries there is no clear-cut answer, so I will just go with it depends. Basically Google does not use meta keyword tags any more at all. So if you are only tensed about how your website ranks on Google then you should not bother using meta keyword tags. They are not important then.
However if you want your website to show up on other search engines like Yahoo! and Bing then my dear meta keywords tags are very important. Yahoo and Bing have a combined ten percent share of search market which might not seem much at first glance but my dear this accounts for 4.6 billion searches each month in the United States alone.
Yahoo has stated in the past that they have stopped indexing meta keyword tag but they offer advice on improving one’s search position including; utilize a keyword meta tag for listing keywords for each page of one’s website. Utilize distinct lists of keywords which relate to each particular page on the website. Do not utilize one broad set of keywords for the whole website. Bing also offers akin suggestions in their head tag optimization blog.
So if you care about your website’s position on Yahoo! or Bing then follow please their advice, but like any search engine optimization technique you will require more than just a good meta keyword tag for getting a good ranking on any search engine.
Cheers to your online success!!