Yesterday, I dist-upgraded our home computer to Ubuntu 8.10. The installed graphics driver (radeonhd, i believe) did not work with our ATI Radeon HD 2350: I got a blank screen. Setting the driver to 'vesa' did work.
After a user switch however, the colors would be messed up. This happens when using the "fast switch user" option, not when logging out and loggin in as someone else. Fast user switching is very convenient when I am playing music on Amarok, and H. wants to read her e-mail. There's plenty of literature on messed-up colors at launchpad.
So i went looking for the right driver. It seems that 'radeon' is the one that should work, but for some reason it doesn't. After trying the drivers 'ati', 'radeon' and 'radeonhd' with varying xorg.conf files, i finally installed the proprietary 'fglrx' driver, which worked.