EliteBastards have an interesting article on NVIDIA's OpenGL anisotropic filtering. Here's an excerpt:

From our testing using the handful of popular OpenGL titles on the market, it appears that the driver issue in question isn't quite as simple as it perhaps first appears. Certainly, for starters, it doesn't seem to affect every game, with The Chronicles of Riddick behaving as expected throughout. Secondly, even in the titles we tested that were affected, the bug only appears to affect the drivers when anisotropic filtering is forced via the control panel. 3D Center's own testing also took in Serious Sam 2 and Unreal Tournament 2004, but as these games both use Direct 3D as their primary rendering mode, I refrained from using them as well, instead focusing on titles that will be played in OpenGL in real-world scenarios.

So, from what we've seen, thankfully this issue doesn't seem to be as serious as it potentially could have been - Most reviewers (and hopefully enthusiasts) will always use in-game settings to control anisotropic filtering where it is available (Which, let's face it, is the majority of modern games), and thus for the vast majority of users neither image quality nor benchmark results have been compromised by this bug. Add to that the fact that not all OpenGL titles seem to be affected, and I think it's safe to say we can avoid reaching all-out panic stations regarding any dodgy 'optimisations' or the like.

Of course, that doesn't alter the fact that it is a little worrying that this driver issue has prevailed for so long (since ForceWare 66.72 according to 3D Center) - Hopefully NVIDIA will move quickly to resolve this bug in a future driver release to quash any lingering doubts anybody may have about the issue. For the time being however, the best advice for anybody wanting to play OpenGL titles in High Quality mode on a NVIDIA board is to use in-game filtering options whenever possible, and failing that, to ensure that all of the optimisations listed earlier in this article are turned off and applied before entering High Quality mode in NVIDIA's driver.