In this article I will show you how to install MDM 1.2.5, the new display manager from Linux Mint, on Ubuntu 13.04 Raring Ringtail, Ubuntu 12.10 Quantal Quetzal and Ubuntu 12.04 Precise Pangolin.
$ sudo add-apt-repository ppa: nilarimogard/webupd8
$ sudo apt-get update
$ sudo apt-get install ubuntu-mdm mdm-themes
During the installation you will get a window asking you to choose your default DM, like the one in the print screen. Choose MDM.
Reboot and login. This is it.
If you are not happy with MDM, change it back to lightdm:
$ sudo dpkg-reconfigure lightdm
If you want to keep LightDM, you can uninstall MDM, with this commands:
$ sudo apt-get remove ubuntu-mdm mdm-themes