id Software's John Carmack made a Slashdot post to a thread called Futuremark Replies to Nvidia's Claims (thanks Jacek Fedoryñski) with some reflections on what does and does not constitute cheating relating to a discussion of the recent controversy (story), as well as a bit that offers some insight into video performance in DOOM 3:

The significant issue that clouds current ATI / Nvidia comparisons is fragment shader precision. Nvidia can work at 12 bit integer, 16 bit float, and 32 bit float. ATI works only at 24 bit float. There isn't actually a mode where they can be exactly compared. DX9 and ARB_fragment_program assume 32 bit float operation, and ATI just converts everything to 24 bit. For just about any given set of operations, the Nvidia card operating at 16 bit float will be faster than the ATI, while the Nvidia operating at 32 bit float will be slower. When DOOM runs the NV30 specific fragment shader, it is faster than the ATI, while if they both run the ARB2 shader, the ATI is faster.