Have you ever needed to remove something from Google? Matt Cutts has a new video over at Webmaster Central that explains the best ways of removing content from Google. Robots.txt or nofollow or both or other, you will find the answers here. http://googlewebmastercentral.blogspot.com/2008/01/remove-your-content-from-google.html
This really isn't anything new, most webmasters know the 3 ways to remove content.... 1. robots.txt 2. robots meta tag 3. via google webmaster's central