For example, I use my gmail ID to log into SO. What happens if I delete my gmail account?
a. Will I be notified that I am using it to log into SO as well?
b. What if I want to delete my gmail account but still want to use my SO account? From a ‘dumb’ users perspective will I have to jump through hoops to be able to do this?
c. etc?
EDIT: Why would someone want to close this?
You should read Rob Conery’s experience using OpenID. You may not agree with it, but it does provide food for thought.