Both Anandtech and HardOCP are recommending AMD CPUs for Doom3. Good news. Also notice that Sempron 3100+ slaughters a lot of Intel CPUs beyond Celeron D's. Like Prescott and Northwoods around the 3GHz mark. 'mas' should be pleased.
Keith, given the strong performance of A64 on Doom3, the better performance on Prescott over Northwood, and the lackluster performance of Athlon XP, one can conclude that Doom3 is rather sensitive to memory latency. Hence the reason why on-chip memory controllers and large caches win out over everything else.