Well, I am running Aperture on a first gen. MBP, with 2 GB of memory. It runs OK, although I am usually careful to shut off all of my other running programs while running Aperture to get the best performance. It is acceptable, though; although I was drooling over the new 3GB memory option on the newer models! Having seen it run on my machine, I can imagine that it would really slow down your G4; but it does run pretty good on mine. I have got to think that with 3GB of memory on those new machines it would run very well. Good luck with your purchase, those new machines look great!