maybe an easy question but let me explain what we did, yesterday we put live our new 2 esx 3.02 servers dell 2950 with dual quad core processors.
we have disabled hyperthreading in de bios because in the early days of esx vmware advised that we shouldnt use hyperthreading.
but, now'r days...is this still the same? or do we need to enable hyperthreading to gain that extra little performance?
in a typical HT aware application the HT process on the CPU processes multiple threads simultaneously which gives you a slight edge in performance as the CPU is being optimally utilized.
In the case of ESX 3.0 kernel the cpu is time sliced. that is each VM gets a time slice of the available CPU. In your case you have quite a few logical processors( each core is seen as a logical processor by ESX) which will never over load the cpu (unless you intend packing a lot of virtual machines into the HOST or configure more than 1 virtual cpu for heavy applications). Enabling HT will really not help in this case.
The new Intel Core architecture has a much shorter pipeline than the previous Netburst architecture. HT allowed the longer pipeline to be more efficiently utilised but with the newer pipe line it is no longer required, thus why it is not implemented.