A Jojo implementation of the SimpleCloak script for WordPress found at http://www.seoegghead.com/blog/simplecloak-v2-php-implementation/

This is not a trivial change to your website, so make sure you read and understand exactly what is being changed.

This plugin adds noindex,nofollow meta tags to every page of the website, unless the visitor is a known bot such as Googlebot.
The decision as to whether a visitor is Googlebot is made by doing a forward and reverse DNS lookup on the visitor IP.

Please read the following links for more information...

http://www.seofaststart.com/blog/google-proxy-hacking
http://googlewebmastercentral.blogspot.com/2006/09/how-to-verify-googlebot.html
http://www.seoegghead.com/blog/seo/how-to-guide-prevent-google-proxy-hacking-p210.html
http://www.seoegghead.com/blog/simplecloak-v2-php-implementation/

Big thanks to Dan Theis and Jaimie Sirovich for the scripts, and the writeup.