I am using Ubuntu 11.04 Alpha 3, running on a Toshiba NB205 netbook. I made the USB drive bootable with the latest UNetBootin for Windows.
I commonly switch between Windows (on the internal HDD) and Ubuntu (on a 2 GB Live USB drive). About half of the time, Ubuntu takes a much longer time to boot up, and after it does, it simply displays a blank screen with nothing but the mouse (working) and the desktop image.
I have found that several re-boots and switching of USB ports on the netbook fixes the problem. After that, everything works.
Perhaps someone high up in the Ubuntu kingdom fix this? It's very annoying.