In the case of google and stackoverflow, instead of using this: http://www.google.com/accounts/o8/id http://www.google.com/accounts/o8/id or http://www.google

In the case of google and stackoverflow, instead of using this: http://www.google.com/accounts/o8/id http://www.google.com/accounts/o8/id or http://www.google.com/profile/kilimanjaro http://www.google.com/profile/kilimanjaro which I never remember, how about just providing username@gmail.com and let gmail.com/openid/username do the magic? Never put the burden on the user...