As an AMD fan, I suspect that AMD processors will be at a disadvantage, since all existing HT-enabled software is optimized for the P4, so AMD loses 15-20% of its maximum performance.
Have you seen the dual core opteron benchmarks? I am an AMD fan too, and I'm not worried with the performance. (I am worried with the price)
Also note that only the extreme edition will be using hyperthreading, the normal dual core pentiums do NOT have hyperthreading, and I think we all know what happens to P4's without hyperthreading...
The hyperthreading on AMD dual cores was discussed around here few days ago. No one came up with a particular reason why it was enabled. I've looked around a few forums and I gather that it has to do with a few old(er) programs that are optimized for hyperthreading but not multiple cpus. They check the hyperthreading capability, if verified use 2 threads, if no hyperthreading is present they don't check the number of actual cpus and use a single thread. It is there to boost performance on these (stupid in my eyes) programs.