As I reported on Launchpad: https://bugs.launchpad.net/ubuntu/+source/gdm/+bug/524497

There’s a usability issue with the login screen’s panel being at the bottom of the screen. It should be at the top, or at the very least the elements that are present in both the login screen and the desktop (the clock and shutdown menu) should be positioned consistently. It’s very confusing as it stands, with the clock and the shutdown function jumping from the bottom of the login screen to the top of the desktop screen when we log in.

Either the top of the screen is the accessibility-wise better place for these elements, in which case they should be there *during the login screen also*, or it isn’t, in which case they shouldn’t be there when we get to the desktop *either*. They shouldn’t be in one place on one screen, in another place on another screen.