1. This tag does pretty much nothing unless the content is noindex or nofollow.
2. I can think of about 30 search engines that once used this tag. it was abandoned to my knowledge over 6 years ago.
3. There was a time when you couldn't surf the web without coming across a SEO page that told you to do this. SEO's back then used to think that was all you had to do until search engines got wise. You can't find these pages now because they have either gone, been changed are don't get listed in the search engines because the page uses that technique.
4. All I have to say is Altavista. Altavista was the major se that used this tag. It was an extended description tag. It's now redundant.