Two of the open source drivers (radeonsi and nvc0) support OpenGL 4.1 now (though only if you've got a bleeding edge build of Mesa, built against bleeding edge

Two of the open source drivers (radeonsi and nvc0) support OpenGL 4.1 now (though only if you've got a bleeding edge build of Mesa, built against bleeding edge LLVM). This is obviously still pretty far behind, but at least it's caught up to OS X. The performance of radeonsi isn't terrible (though that's partly because the proprietary AMD driver sets the bar kind of low), though still generally slower than the proprietary one. There are some experimental instruction scheduling changes in an LLVM branch that appear to give better performance than the proprietary drivers for at least some benchmarks. On the Nvidia side it's pretty much proprietary or bust though. Featurewise it tends to be in good shape (at least in comparison to the other open source drivers anyway), but there's no support for changing the GPU clock so performance is terrible.