Two part discussion of Aperture 2.0 at ApertureProfessional.com; discusses changes to the app and their implications.
Part 1 Part 2
Another nice write-up on how Aperture 2 has evolved is
this one from Rob Galbraith.
I've been playing around with Aperture 2.0 off and on over the last 24 hours, and I'm most struck with by the better organization and presentation of the interface. In addition to lifting a couple features from Lightroom for image adjustment, the interface itself now exhibits more characteristics of both Lightroom and iPhoto '08. Less space is sacrificed to "administrative debris" (although there's still plenty room for improvement) and with three keys you can cycle through all the really important view configurations. Overall, the user interface is certainly more comfortable
for me than past versions. The only area that seems a step backwards is the web gallery features: it seems Apple decided to throw out what they had going and drop in what is basically iPhoto '08s web gallery features that depend on .mac service.