I think it is complicated in that you are put in front of so many buttons and choices, whereas before it was one way: username and password.

This is probably the main user friendliness issues with openID. It's made worse by the fact that your Google/yahoo openid is some long URL and that typing in your yahoo/gmail in an openID 1.0 box doesn't redirect you to the login page like an openid 2.0 box.