Phoronix checked out the state of AMD Linux driver development, you can check it out over here.
"Earlier this week Sapphire launched the Radeon HD 5830 Extreme
using the well-supported "Cypress LE" graphics processor at a very
competitive price relative to the NVIDIA competition and the Radeon HD
5830 graphics cards from other AMD partners. With it being part of the
HD 5000 series and not one of the newer HD 6000 series graphics
processors, the Linux support is already spot-on for both the official
Catalyst Linux driver and within the open-source stack. In this article
are the open-source Gallium3D benchmarks for the Radeon HD 5830 along
with other recent ATI/AMD GPUs to show where the latest Mesa/Gallium3D
code is at today."