Bigger ISO file size
With 12.04 LTS, it's bye bye to CDs. The ISO size will be 750 MB so you have to rely on USB drives and DVD to burn ISO. From 12.04, 64-bit version of the OS will be the default download option.
Unity will continue as default interface
Given the generally positive reception that Unity interface has received, Ubuntu 12.04 will have Unity as the default interface. You will have option to install other WMs via Synaptic Package Manager and/or Ubuntu software center.
Cloud based login
Similar to how Windows 8 allows you to use your Live account to login to Windows, Ubuntu will allow you to use your Ubuntu One account to login to account. This way, all your settings and files will be synced to the cloud and you can login to any machine and you will have the OS set the same settings and also access those files in your home directory.
Other feature include improving software center, GNOME 3.2 option over 3.4, Banshee back as preloaded media player.