Phoronix tested AMD's Fusion platform with Gallium3D on Linux and reports the experience wasn't that great, you can read about it over here.
It's been a few months since last running any AMD Fusion tests
under Linux, so here's a look at the AMD A8-3870K "Llano" APU
performance under both the latest Catalyst driver and the open-source
Radeon Gallium3D stack with Ubuntu 12.04. Besides the open-source driver
being handily beaten by the Catalyst binary driver, the power efficiency
is also a disappointment.