64-bit will pretty much be a universal standard, likely before 2010 (just my guess).
Tangent:
One of the nice things about the latest Mac OS (Leopard) is that you don't have to choose a special version. There is exactly one version (not counting Server), and it is BOTH 32 and 64-bit.
yup, and the latest Mac Pros come with bootcamp drivers for 64 bit MS OSes
OS X 10.5.2 is shaping up to be a nice little update:
http://www.appleinsider.com/articles/08/..._5_2_build.htmlalso, Nvidia working on GPGPU for the Mac:
http://www.appleinsider.com/articles/08/01/24/nvidia_working_on_first_gpgpus_for_apple_macs.html