This looks sucky for CS4, but the long run this is actually a good thing. Consider this: Apple is basically deprecating Carbon and forcing Adobe to move to Cocoa.
So yes, we will have to wait an extra 18-24 months for 64-bit Photoshop. But the upside is that the Mac versions of CS5, CS6, CS7, etc. will all be poised to take advantage of all the new technologies Apple introduces over the next decade (think resolution independence).
Meanwhile, the Windows versions of CS5, CS6, CS7, etc. will STILL be stuck on Win32 (yes, ironically the 64-bit API is still called Win32), just like 99% of the rest of Windows software. This is a horrid API that basically dates back to Win 3.1 days, and there is no way that CS (or most of Windows, for that matter) will be getting features like resolution independence.
Bottom Line: Apple is forcing an 18-24 month delay in 64-bit CS by deprecating Carbon, but this move will pay off over the next decade as CS can immediately take advantage of all the new features OS X introduces. CS for Windows gets 64-bit support 18-24 months earlier, but it's not going to be positioned to adopt any new features over the next decade.