"OpenID starts with the concept that anyone can identify themselves
on the Internet the same way websites do-with a
URI
(also called a URL or web address). Since URIs are at the very core of
Web architecture, they provide a solid foundation for user-centric
identity."
With major sites like Digg announcing support for OpenID, it seems it may not be long before a single-sign in world is upon us.
Read more about OpenID here.