Elite Bastards has posted an analysis on NVIDIA's OpenGL anisotropic filtering

The specific questions being asked this time around are with regard to the way NVIDIA's ForceWare drivers handle anisotropic filtering in OpenGL titles, more specifically when the drivers are set to work in 'High Quality' mode (i.e. with all optimisations disabled). German web site 3D Center broke the story, pointing out that running OpenGL titles with all filtering optimisations manually disabled resulted in lower performance (and better image quality) than simply using the driver's High Quality mode to disable these optimisations automatically. Naturally, this has led to accusations of NVIDIA artifically inflating performance, benchmark scores, and so on - The usual cries when any driver bug which increases performance to the detriment of image quality is discovered these days, particularly given NVIDIA's past history.

Elite Bastards analysis: NVIDIA's OpenGL anisotropic filtering