I think your ‘best case scenario’ is a bit misleading. Real best case is that without even registering at all I log in with an OpenID, click ‘allow’ from my provider and I’m in to a brand new account on the site in question. As we as developers get more comfortable and experienced with the technology, I think that sort of user experience will be more commonplace. Just give it a little time to bed in.

One real tangible “normal user” benefit that I don’t believe you’ve mentioned is the fact that OpenID users don’t need to go through the whole choose-an-available-username hoopla that is frequently the most time-consuming and frustrating part of signing up to a popular service. Early adopters often forget how miserable that experience is because they’re signing up at a point where their first or second pick of username is still available. OpenID is a great solution for that.