I have the same problem.
My arduino uno works well on my Mac and in windows 7 on parallels.
But on my desktop with Ubuntu 10.04 no!
I use 10.04 because is the LTS version.
The  launchpad.net/~arduino-ubuntu-team/ version is a old version and don't have Arduino Uno interface.
After i connect arduino to USB Port and open 0021 the menus, like tools, are really slow to open. More than 15sec..