Det här läste jag hos searchenginewatch:

In Conclusion
Overall, just remember this. Of all the meta tags you may see out there:
Meta Robots: This tag enjoys full support, but you only need it if you DO NOT want your pages indexed.
Meta Description: This tag enjoys much support, and it is well worth using.
Meta Keywords: This tag is only supported by some major crawlers and probably isn't worth the time to implement.
Meta Everything Else: Any other meta tag you see is ignored by the major crawlers, though they may be used by specialized search engines.

Det får en att tänka efter lite!