It turns out that Nvidia is not doing anisotropic filtering the way it should and that the picture quality is the one to suffer. You will get the shimmering effect on your textures whenever you are using Geforce 7800GTX cards but you won't see this using Radeon cards.
The guys claimed that all NV40 and G70 cards will suffer from the same flickering problem and that these cards have "by far worse AF quality". They also add that Nvidia got the flickering because it was using general under sampling and as a result is getting the flickers. It's interesting to note that older Geforce 5800 Ultra won't suffer from this, just the new cards that 6800 or 7800 based.