Actually for HT, you do want to program for it. Just telling it that you have more cores is a fiasco because you'll end up scheduling too many threads to one core while other cores are sitting idle.

Remember that with HT, 2 cores do not execute at the same time, one has to wait for the other. So if you had a quad core with HT and you wanted to schedule 4 threads, you would put them all on different cores for the best speed. If you just said take the first 4 cores, you would get two threads sharing the first core, 2 sharing the second, and two idle cores.

In a server workload, HT gives you a 10-20% increase in throughput, so do you want 2 threads sharing for that 10-20% increase, or do you want all of your threads on individual cores?