Goodluck - others have experimented with this but I don't know of any existing service right now. There's a great novelty factor involved with a "email-to-signup" flow but I agree that that's a bit awkward for many users. One cool idea is a twist on that - use an OAuth signup process with FB/Twitter and send a cool confirmation postcard to the user's address they have listed on FB, etc - depending on how to word it there's a viral element to it.