Same issue on Compaq Evo N610c (ATI Mobility Radeon) with Lubuntu 10.04. It works again if I disable KMS (which also fixes Bug #567957). You can add "nomodeset" to the kernel command line in Grub or make it permanent in GRUB_CMDLINE_LINUX_DEFAULT of /etc/default/grub and then run update-grub.
Same issue on Compaq Evo N610c (ATI Mobility Radeon) with Lubuntu 10.04. It works again if I disable KMS (which also fixes Bug #567957). You can add "nomodeset" to the kernel command line in Grub or make it permanent in GRUB_CMDLINE_ LINUX_DEFAULT of /etc/default/grub and then run update-grub.