The keywords meta tag is dead, and that since 2001, but many webmasters and (strangely enough) SEOs still insist on its importance. And for a good reason. Although ignored when technically correct, the keywords meta tag will lead to search engine penalties when you use it for keywords stuffing.
But when it comes to blogs the keywords meta tag is more than relevant, especially when it is associated with a smart plugin that transforms your keywords automatically into tags.
This plugin is one of the best WordPress tools you can get. Used wisely it will even boost your technorati traffic, by transforming your meta keywords into technorati tags that appear on the technorati tag pages. A good reason to have a keywords meta tag and even a better reason to install a smart WordPress plugin. For other types of blogs (like blogger) there are other widgets and plugins available, and in their absence you could always read the help pages on technorati to learn how to create a technorati tag. Use these tags to raise the value of your blog within the technorati hierarchy.
To make a long story short: the keywords meta tag is not dead. It just changed its clothes and functionality. Use it wisely and it will prove its value in no time. Abuse it, and the joke is on you.
Another WordPress plugin you might be interested in: Ultimate Tag Warrior – particularly interesting as it allows you to get suggestions for tags using the Yahoo! keyword suggestion service from the write post page.