Interesting post from SearchEngineLand.com on a test conducted in Yahoo regarding support of the meta keyword tag. Yahoo was supposed to have dropped support of the tag but this test and one I conducted might prove otherwise. I went to Yahoo and entered a misspelling of leukemia and found one of our clients as the top result. The only misspelling of the term is within the meta keyword tag.
So would I go as far as saying the meta keyword tag is important and make sure you have all of your keywords in it? No, but I would say it can be used to help with terms that might have less competition like a misspelling.