Along with all the good responses to your question, it's worth pointing out that Intel has completely open-sourced their driver and GPU, and ATI has open-sourced their GPU and produced a driver that can do about 90% of what the closed-source driver can do.
P.S. Broadcom open-sourced a part of their GPU for the Raspberry Pi. (Specifically the VideoCore IV VPU on the BCM21553 which RasPi is porting to the BCM2835 http://www.raspberrypi.org/a-birthday-present-from-broadcom/ )