A new GDM that uses OpenGL has been discussed and ideas have been thrown around. The project didn't make it into Intrepid, but hopefully we will see this new feature in the next Ubuntu release. It would help Ubuntu raise the bar and exceed the expectations. Of course this is again the work of Mirco Müller. Here is a link for the specs: https://wiki.ubuntu.com/DesktopTeam/Specs/GdmFaceBrowser
As you can see below, two previews have been released:
The login via GDM is meant to default to a face-browser allowing simple point-and-click user-selection. Only the password-entry will require the user to use the keyboard. It is still possible to type in the login-id instead of selecting the user with a mouse-click on her/his image. This will also cause the set of displayed user-faces to be filtered to the remaining completion-possibilities, thus rendering the remaining images larger and making the hit-area for a mouse-click even bigger.
The official name of it is "Login Experience" now, not "Face Browser" anymore.
Read Mirco Müller own blog post here: http://macslow.thepimp.net/?p=163