Use oath or Google Contacts API to get friends email addresses

Google Contacts has an API to allow you to get contact info from my Google account without my having to give out a password. 
http://code.google.com/apis/contacts/docs/3.0/developers_guide.html

While I'm sure you're all trustworthy and stuff, I still don't like giving out my Gmail address just to find out if friends are using your site. I would very much prefer if I could use the secure method.