When you publish something, you of course want page rank, but you also want people to be able to find and use what you publish. It looks like you are considering only keywords when considering meta tags, and I think that is a mistake.

Language, description and author are equally important. Since it costs only a few lines of HTML to include that, I can't find a good reason not to use them.

Its wise to not just consider search engines when deciding what goes into any given document. The knowledge that the tags are standard and something might look for them is (in my opinion) motivation enough to include them.