I like the idea, at least partially. It's a heck of a lot better than the cold gray/blue wash that OS X presents. I really dislike designs that make the whole system look the same. Each app should look unique and separate from the underlying system UI. The whole "lets wear matching UI's" phase lost it's appeal around the same time that the second Matrix movie was released.
Now I think that making an app look like a real life physical object that is only loosely related to the basic theme or concept of the app, well thats cheesy, at least when it's taken as far as apple takes it. In the app I am making for iOS, it's a midi controller app, I take elements from real music related hardware. I've styled the ui's buttons after the kind you would find on an old electric organ with many different pastel colours set on a textured black plastic with white screen printed labels. Many of the buttons light up when activated and reflect off the black plastic backing. The borders are a thin raised metal strip. It all looks quite nice, but it also looks nothing like an electric organ, that would be silly, it's a midi controller.