Permlinks in Email and others

Permlinks is widely used in Web2.0 applicatoin like social bookmark, blog, wiki …etc.  It is useful as permanment reference can be made by simplily include the URL.  The similar concept is moving to other application like calender, event organizer … etc.  Biz Stone proposed to further extend  the usage to email and other collaboratioin tools. 

Using email as example, Lukas agrued that such may eliminate the privacy nature.  What if we add authenticating / authorizing feature, i.e. the permlink is available only to people authorized.  Technically, authentication + authorizing + retrieving content can be done with web service.  The problem now is how to identify people in an open envrionment.