Comment 16 for bug 570589

Julien - poor hardware design is a possibility. Also make sure you have removed all dust from inside the computer, particulary from the CPU and GPU fans and heatsinks (if it's a desktop, open the case, if it's a laptop at the very least run a vacuum cleaner nozzle along the external air vents). You can also put the edge of a book under the back edge of your laptop so that it is raised off the desk at a slight angle, or purchase a laptop cooling pad (with USB powered fans) to sit the laptop on.

I neglected to mention that to use the new power management feature on R700 and newer hardware (other than APUs) requires installation of the latest AMD graphics microcode (ucode) files to /lib/firmware/radeon
These are available at http://people.freedesktop.org/~agd5f/radeon_ucode/
Get the version ending in "smc".