Unity Greeter 0.2.4 (the LightDM login screen theme) has been uploaded to the Ubuntu 12.04 Precise Pangolin repositories and it comes with a cool new session chooser dialog (screenshot above) which replaces the old menu.
The login box was updated too:
You can see the latest Unity Greeter in action below:
(direct video link)
The new Unity Greeter should be available as an update for all Ubuntu 12.04 Precise Pangolin users in a few minutes/hours.