I've been playing with a similar idea - http://appworthy.co

One thing I've done on my site is abandon passwords. Authentication is by email (if you can receive a link you can "sign in" once with it - thereafter cookies).

This avoids the need to ask for permission (to tweet for me? really?) up front. Users can start reading and posting without giving up anything but their email.

This is not a new idea, but I think it works well to minimise barriers for potential contributors.