With the 4.5.0 release Qt gained 64-bit support on OS X using the Cocoa framework. The Mac binary package remained with Carbon for backwards compatibility, but at the same time there was no Cocoa binary package. This is probably extremely bad marketing on the Mac team part (creating a new feature and then not making it easily accessible), but then again none of us were hired for our marketing abilities.
So without further apologies, here's a test version of the open source binary Cocoa package. The package is not officially supported. If everything goes according to plan, we'll have supported commercial packages available for 4.5.1.
The package contains an universal build for 32/64/ppc/intel systems running OS X Leopard or higher. Four architectures is probably a bit too much for a binary package (the debug libs weigh in at 500 MB). x86_64 is here to stay, but which of the others should be removed? Leave a comment and we'll see who gets voted off the island.