Creative Suite CS4 gets support for 64-bit but only for Windows
The program package Adobe Creative Suite CS4, which includes Adobe Photoshop CS4 among other programs, are planed to get 64-bit support. This means that Photoshop will be able to handle more internal memory in the computer, which means better performance and the possibility to work with larger photo files more effectively.
Mac will probably not get support for 64-bit until Creative Suite CS5 is produced due to technical difficulties.