In the end, Apple made the hard choice instead of the easy one. I think it will pay off, though the short-term consequences could be pretty grim. After all, just look at how long it’s taking to get an Intel-native version of Microsoft Office for the Mac. Should we expect a 64-bit Cocoa version in, say, 2012? And I have no idea what Adobe’s going to do about 64-bit versions of its products. That’s many millions of lines of Carbon code between those two companies alone. We may be in for a rough patch, so buckle up.
— John Siracusa on Leopard’s Cocoa-only 64-bit support in GUI libraries (geek level: 97%)