Title and description tags are important. Keyword metatags are a complete irrelevance, major search engines don't use them http://googlewebmastercentral.blogspot.com/2007/12/answering-more-popular-picks-meta-tags.html http://www.google.com/support/webmasters/bin/answer.py?answer=79812&query=meta+tags&topic=&type=
Title is the main keywords describing the content, should consider what it Meta Description described as attractive to viewers, it is a question logic
The meta tags are known to not be used by most of the major search engines. But it's always a good idea to include them just in case. You never know when a search engine may decide to factor in meta tags again!
from what i have read if you are not careful with Meta Keywords then your site rank can go down... in search engines and not having them doesnt hurt you so why use them?
Meta tags are very important . Title and description tags are the most important. They tell search engines what your page is about and help you get ranked better.
only meta description with combination of first 200 word of page start and alt in IMG define your target keyword (ofcource with title and site address)