I finally finished looking at all the "quick tour" movies about Aperture, and the photographer profiles. It took a few days because every time I watched one of the quick tours I nearly had an orgasm.
I think Aperture is going to drastically change things in digital photography they way iTunes changed the way we buy and listen to music. This is truly one killer app. When I first heard about it, I thought $499 was too much. But, now that I've seen the depth of the program and the incredible features it will offer, it's well worth the money.
But I don't think it's going to be a Photoshop killer. Photoshop has lots of features Aperture doesn't, and vice-versa. There is some overlap in features, but, all the airbrushing, photo-correction and retouching tools are still needed. Plus, PS has become an important tool for creating web graphics, with tools for scaling, sharpening, saving in various formats and combining vector graphics with bitmap graphics in layered documents. So, I don't think PS is in any danger of being shoved aside by Aperture. You can't use Aperture to design a website interface.
But for digital photography, I think Aperture will set the new standard and become the tool digital photographers have been waiting for for years.