Matt Cutts of Google, and Google itself have now officially announced that they do not use meta keywords at all mostly due to past abuses, and with Google having over 83% of the search engine market share as of October 29, 2009, they are the ones you need to pay attention to. The breakdown:

1. Google – Global 83.13%
2. Yahoo – Global 6.84%
3. Baidu 4.38%
4. Bing 3.39%
5. Ask – Global 0.58%
6. AOL – Global 0.55%
7. AltaVista – Global 0.08%
8. MSN – Global 0.06%
9. Excite – Global 0.02%
10. All the Web – Global 0.02%
11. Lycos – Global 0.01%
12. Microsoft Live Search 0.00%

Matt Cutts also mentions that meta description does nothing to increase SEO, but if you have it, they may use it as the snippet in search results for a particular site, page or post.

Bottom line? Spend your time creating high-quality original content, use appropriate categories and tags on your posts, use descriptive titles and don’t worry about meta tags. They simply aren’t worth your time.