I think that people might underestimate what effect Aperture (again, assuming it REALLY works as advertised) will have on working digital photographers.
We all have our preferences - while we all like a nice selection of lenses in our bags, if you had to take only ONE lens on a body for an extended shooting trip, you'd make those preferences quite clear. Some might prefer a telephoto for reach, while other (including myself) would opt for a wide angle for my style of shooting. Not right or wrong, just my preference.
The same holds for our software - if we could only take one program on a laptop for an extended shoot, what would it be? Until Tuesday, I'd have had to answer PS. Despite the frustrations in handling large quantities of images, its pluses outweighed its minuses.
But has Aperture changed that equation? If it performs as planned, I WOULD take Aperture's work flow, RAW handling, and limited editing possibilities over PS.
It's not too often that I'd rethink my most important lens, and it's not too often I'd rethink my most important digital darkroom tool. That's why this might be an important piece of software.