Aperture on PowerBooks

Apple's new post-production tool for photographers, Aperture, is one of the most promising applications to come along in a while and it has the potential to revolutionize photography as we know it. I'm wondering how it will perform on real world PowerBooks in the field.

Apple lists Aperture's minimim system requirements as:
- 1.8GHz Power Mac G5, or
- 1.8GHz iMac G5, or
- 1.25GHz PowerBook G4

Which of these Macs doesn't belong?

It's curious that Apple recommends that Aperture run on 1.8GHz G5's and 1.25GHz G4 PowerBooks. I wonder what type of performance penalty PowerBook users will feel when running Aperture? I can't imagine that it will run nearly as well on a G4 PowerBook as it will on any G5 desktop. The problem is that a great many professional photographers that shoot in the field will want to use Aperture with a PowerBook rather than waiting to drag their memory cards back to the studio to download the images.

I hope that Apple makes Aperture perform acceptably on its current (and previous) crop of PowerBooks otherwise they run the risk of releasing a groundbreaking application that isn't usable for most photographers in the field.