how can one identify bottlenecks in video card driver? i always thought it's nigh impossible.
There are other bottleneck like some GL stuff which are not handled well enough currently (enemy territory use some of this). Anyway there is work underway to address most of pitfall of current open source driver. What is hard is that we need to keep backward compatibility so we endup doing crazy things just to make sure we do not break old things (new drm should work with new Xserver, new Xserver should work with old drm, new dri driver should work with old drm, ...).