[chickopozo]

This has existed for years: http://www.google.com/recaptcha/mailhide/

And your email isn't stored but rather encrypted and the ciphertext passed via the url.

[chickopozo]

http://www.google.com/recaptcha/mailhide/d?k=01eHy-6e8CKpz-d...

k is your id and c is the ciphertext the key is stored on their server.