Anisotropic Filtering Modes and Performance
The Radeon HD 2000 series of graphics card have essentially the same anisotropic filtering abilities as the Radeon X1900 series. The texture units in the HD 2000 series have been tweaked to better handle some problematic texture filtering cases, but real-world performance shouldn't differ significantly from ATI's previous generation.
As you can see in the screen-shots above, as the level of anisotropic filtering is increased, the clarity and sharpness of the ground texture is enhanced. If we compare the quality of the images produced with each card, it's difficult the pick one that is clearly superior the another but there are definitely more subtle detail in the captures grabbed with the GeForce 8800 GTS. If you focus your attention on the cracks in the ground in the distance about 1/3 of the way up the scene, you'll be able to pick up some of the differences.
The images captured with D3D AF Tester also show the GeForce 8800 GTS' strengths. The 8800 GTX has almost no angular dependency and produces smooth transitions, in an almost circular pattern. The Radeon X1950 XTX and HD 2900 XT also do a great job with anisotropic filtering, but if you open the 16X aniso shots taken with the D3D Tester side-by-side you'll see the 8800 produces the superior pattern.
To see how using anisotropic filtering affected performance with the Radeon HD 2900 XT, we fired up Half Life 2: Episode 1 and ran though a series of benchmarks with different levels of anisotropic filtering being applied. Only about four frames per second separated the highest and lowest scores here, so consider anisotropic filtering a 'gimme' with a card of the Radeon HD 2900 XT's caliber.