As you may know, the Ubuntu team is working on a mobile version of the OS for mobile internet devices. But because there isn’t much of this hardware around, the UME builds don’t get the natural community testing that the desktop and server editions do. But if you are interested there is a way you can help! 
The mobile environment can run in a Xephyr window. Setting up this environment is fairly easy and is described in detail here.
If you want to help with structured testing please follow the UME test cases starting with the desktop test. And if you find any bugs please file them under the ubuntu-mobile project in Launchpad.
If you have questions you can usually find cgregan, davmor2 or myself (heno) in the #ubuntu-testing channel. Have fun 