This one time, at band camp, James Green wrote:
It occurs to me that there's very little point in search engines crawling certain pages of an OpenGuide - anything with "action=edit" or "action=delete" in the URL, at the very least, has no real value to someone searching for information. Unfortunately, unless I'm missing something, robots.txt syntax doesn't allow for matching on anything other than the start of the path component of a URL, which doesn't help us here.
Solution here would be to change the syntax of the action= URLs to be something like: /action=edit/MyWikiPage
Then you could put /action=edit/ in your robots.txt file.
This would probably, if you're not already doing it, involve Apache rewriting which, if you're not already doing it, be a bit more effort than is really warranted.
Using the meta tag doesn't remove the problem of the bandwidth used.