Rage3D has done it. They found the first DirectX 10.1 game and they have tested said game with a HD 2900 XT and a HD 3870 X2. Want to know what game it is? You'll have to read the article to find out!
Here is a statement from an ATI employee that confirms Rage3D's discovery:
"...In this instance our developer relations team worked directly with the developer and found an area of code that could be executed more optimally under DX10.1 operation, thus benefiting the ATI Radeon HD 3000 Series."
Ubisoft is removing the DirectX 10.1 support from Assassin's Creed! lolz!