The OpenID authentication page provides a “Stay signed in” checkbox.

Is this checkbox for developers to use so they can implement their own bookkeeping, or is it only used by OpenID itself? After a little while of playing around with it, I don’t see it making a difference in anything on Stack Overflow.
I’m pretty sure that it just modifies whether myOpenID will remember your session for the next time you authenticate against it – if you don’t check the box (test by going to https://www.myopenid.com/ and clicking Sign Out), then when you log out and back in, you’ll need to retype your password, whereas if you leave it checked, then you can log out and back in without a password.
(In short, it has nothing to do with OpenID itself and just has to do with the myOpenID session itself.)