I am also new to this list. I subscribed because the commercial driver gave me a lot of trouble. I have a Radeon Mobility 9700. The main reason that the driver didn't work out for me, was that my bios filled out the mtrr space (that's what I understood, I am not that technical), and my bios doesn't allow me to do anything towards solving this.
So before I start testing this driver, I want to hear your oppinion on this issue, regarding if said problem will also limit the possibility of 3D acceleration which may be available in this experimental driver.