The only meta tag that is important is the description meta tag. And title tag is the other important tag to use. Other than these two, all order tags are not important. Especially, keyword meta tag is useless.
It wont hurt you to have meta tags inyour sites it will certainly help you in msn and other search engines
I had a recent site built and I completely omitted the keyword tag. The only downfall is it takes Yahoo eons to index you because they still use them. I would suggest using them anyway, just don't spend too much time adding them.
It still works with the less known engines Inktomi and Teoma, but Teoma supports it "unofficially". What about what Danny Sullivan said: "Death Of A Meta Tag" First read it and then get over it.
Meta keywords are not important to improve PR it is important to ranking point of view. But meta keyowrds not rely on ranking factors actually. If in meta tag keyowrds density is maximum then page will be count as a spam of keywords density.