Does the "Remember Me" button do anything?

I’d expect the "Remember Me" button on the login screen to (if checked) set a cookie to remember the username - so the next time the user visits that page, the username field is already completed.

I haven’t been able to get it to do this - on Firefox 4, Chrome, or IE(8) - whether it is ticked or not the username is never prefilled, and I can’t see a cookie being set which might be remembering it.

Have I misunderstood, or is there a problem with it?