I've just recently gotten DRM working with a ATI Mobility 3650 (r600) on Debian in a Thinkpad W500. I've read that power management wasn't support when running KMS. So I've turned off KMS for the time being. I have the following options in my xorg.conf file:
Yeah some code to lower voltages would be nice, but lowering clocks does make a significant difference here. I haven't yet found a way to measure temps but I see a difference of approximately 20W in power consumption and also a significant reduction in fan noise here.