MSAA is needed for GL3 compliance and is generally expected of modern GPU drivers in 2013. The R600 Gallium3D driver has had MSAA support for a while now and finally it's come to RadeonSI, the Gallium3D driver for AMD Radeon HD 7000/8000 series graphics cards.
A set of 20 patches posted this week by Marek implement MSAA rendering, texturing, and color-buffer compression. Still to be done though is MSAA fast color clear support and on top of the 20 patches there are also some LLVM shader back-end changes needed too. While some of the code was ported from R600g, the RadeonSI patches are implemented for maximum hardware performance.
The current patch-set, which has yet to be committed to Mesa Git for Mesa 9.3/10.0, can be found on the Mesa mailing list.