Red Hat's Matthew Garrett has chronicled his AtomBIOS
hacking adventures on his blog
that has led to aggressive power management capabilities. By using an AtomBIOS program written by Jerome Glisse
to manipulate the clock frequencies, the previously-published R500 documentation, and coding, and he managed to save 10 Watts of power with a Radeon X1300. His yet-to-be-merged DRM code down-clocks the memory frequency automatically when the screen is idle and GPU core down-clocking. Matthew has published this code in his own git repository for early testers.
Also in the power management realm, earlier this year there was R500+ Dynamic Clocks support
added to the open-source ATI driver.