The Fastest Registration Ever: Friend.ly
No wizards. No forms. No Facebook Connect or Twitter Oauth popups. No typing at all.
A single click is all you need to sign up for friend.ly. After that, you’re in, with a profile including your picture. You’re connected to friends. You have pre-filled questions to answer based on your interests, as well as pre-filled questions to ask your friends based on their interests and mutual connections. There’s a leaderboard of your connections. You’re in. One click.

Friend.ly landing page

One click later, the newsfeed
This is accomplished via Facebook’s registration plugin, and I’ve never seen it implemented so well. It assumes you have a Facebook account, and works best if you’re logged in to it. For a social app like this, that’s a pretty fair assumption.
Perhaps that’s why their early traffic numbers are looking, well, smoking hot.
