"High Quality apparently turns off angle-adaptive anistropic filtering"
-- hexus nv40 preview
"NVIDIA was also kind enough to expose a setting in its driver that allows the user to disable its adaptive anisotropic filtering optimizations by choosing "High quality" image settings. In this case, both ATI and NVIDIA use adaptive aniso, so disabling this optimization wouldn't really be fair. Also, I spent some time trying to find visual difference between NVIDIA's adaptive aniso and non-adaptive aniso (using different angles of inclination, looking for mip-map level of detail changes, doing mathematical "diff" operations between screenshots) and frankly, I didn't find much of anything. I did benchmark the two modes, as you'll see in our texture filtering section, but I could find no reason not to leave NVIDIA's adaptive aniso turned on during our tests."
-- techreport.com preview
I'm not so sure that non-angle dependent AF was actually enabled in the Forceware drivers that were sent out to reviewers. This could be why the reviewer found it very difficult to find any pic where there is a difference in IQ.