OpenID

I think one of the big developments of 2008 will be the spread of OpenID.  OpenID is a way for people to have a single sign-on across a variety of websites.  For example, a person wanting to comment on a particular website could login with their OpenID, instead of creating yet another username and password.

OpenID appears to be designed correctly as it is free, decentralized, and not controlled by any one provider.  The big players are signing on as well, as Yahoo just announced they will support OpenID.  I think OpenID is the future of identity management on the net, and it could be quite common by the end of the year.