The idea that we could have one password for all of our web activities is extremely appealing. I can't tell you how many sites I have registered for in the past just to check out their service. Of course, I would expect that we all do the same thing. We try to pick the same user id and password for all of these sites so that our brain does not implode on itself but that is not always possible. What we end up with is an alphabet soup of user id's and passwords in our brains (or on paper). As previously mentioned, OpenID is gaining a good bit of momentum. Remember....this is an open source system that attempts to bring order to the chaos that has become our need to remember hundreds (or thousands) of logins to separate sites. One service...one ID...access to any website. What a perfect world that would be!
We have news today that Google is considering throwing their support behind the OpenID movement beyond just their Blogger platform. I would consider this decision (if it happens) to be the tipping point.