Unlisted Repository

What?

Provide the ability to make a repository as unlisted. It would function just like an unlisted youtube video;
https://support.google.com/youtube/bin/answer.py?hl=en&answer=181547

Why?

An unlisted repository would benefit this site by allowing developers to share their code to a wider, yet known and trusted audience. There exists a space between "This code is so good, I must share it with the word!" and "This code is so private I must only share it with those already invested in it." (and therefore willing to register for an account).

Additionally, frictionless sharing will help drive other developers (the ones that were brought to the site by an unlisted share) to explore and become familiar with the Bitbucket site, and potentially convert them to registered users.