I hope Amazon succeeds wildly with this. Google's App Market is incredibly terrible... just full of so much trash. Plus their lack of testing/verification has led to two separate people selling blatant ripoffs of my app. Google removed them when I complained, but I have not had this problem with Apple's App Store or the Palm App Catalog.
There is also still no way to link people browsing on PCs to your app (other than Appbrain).