Dell has decided to use AMD's opteron processor for its server machines. I never thought Dell would move away from Intel.
I have had several discussions with my friends from Intel and AMD. They are unable to confirm if one is really better than the other. In almost all cases, the choice seems to be on personal experiences of some people. For non-geeky users, perhaps, Dell's loyalty to Intel might have been one of the reasons that people thought Intel was better.
I wonder if it really matters, especially for the non-geeky user. I have used a desktop with Intel and another with AMD processor at my home. I am unable to say one of them is better than the other.