A demo on its site - it requires Flash to view - compares a spreadsheet calculation. That takes five minutes 39.9 seconds on a 3.06GHz Pentium 4 without hyperthreading while with hyperthreading, Intel claims it takes 35.58 seconds.
This is a remarkable feat and leads us to believe that hyperthreading is better than anyone could possibly have anticipated.
Indeed, with the performance of your processor boosted by over 900%, truly no-one should be without one.
You can run the demo from this Intel page, while the Ace's thread starts here. µ