My favorite feature of Jaguar is the speed increase. Even without QE my 500MHz iBook runs very nicely, and will be a very nice machine for the two more years I plan to keep it (I will have had it for a year in 5 days). I will be buying a new tower in January, though. I'm ready to buy my first serious desktop Mac, and I want it to scream. It should have no trouble doing just that running OS 10.2.2 (speculating).