|i have no personal experience with the i7, but ...:|
1) when multitasking, my p4 was faster with HT enabled than without it.
2) the only way you would see a performance increase is if you are running multithreaded apps, or more than 4 applications at the same time. up to 4 applications, and you'll see no added performance benefit. open up 4 more, and THEN you might benefit from hyperthreading.