As the subjects says . . . .Carbon would be the interim tool for the big corporations(Adobe, MS . .) to port their code quickly to OSX. As I recall, the reason why yellow_box never hit on was that it meant totall rewrite of application. And so, for not scaring away developers, carbon were "invented".
Maybe I am really way of here, but I thought that the main benefits from Cocoa was that any Cocoa application would have all the OSX technology "baked" in automatically ( like taking advantage of MP).