One of the changes in the recent Ubuntu 10.10 (Maverick) is the upgrade of Linux kernel from version 2.6.32 (in Lucid) to 2.6.35. The change introduces several new features of which I especially like Radeon power management (for use with open drivers).

Unfortunately the default power profile only saves power when the screen is off (or on battery I think). I also know of no GUI tools to manipulate the power profile. Here is the command I found to change the profile using sysfs:

sudo -i 'echo low > /sys/class/drm/card0/device/power_profile'

The change is not persistent, but the quoted part can be added to e.g. /etc/rc.local to get it every boot. (I'm unsure about suspend, which I don't use.)

My Radeon HD 4850 has enough power for desktop effects at the lowest power level, lower end cards may work better with the mid level profile.

To see current power and voltage info, here's another command:

cat /sys/kernel/debug/dri/0/radeon_pm_info