Snow Leopard in 64-bit mode? Any benefits for FCS or CS4?
 

Does it make sense to run SL in 64-bit mode? I'm wondering if there are any benefits for FCS and CS4. Or are we still waiting for the software to catch up and take advantage of the 64-bit mode?

Snow Leopard runs 32-bit or 64-bit programmes equally well whether running with the 64-bit kernel or 32-bit kernel. It is down to the application itself whether it is 32-bit or 64-bit. Snow leopard itself is pretty much all 64-bit which can be confirmed by running Activity Monitor & looking in the column labelled 'Kind' where all the OS X system processes & applications (Mail etc) are 'Intel (64 bit)'

While most all Intel Macs can run with the 64-bit kernel the only model that boots this by default is the Xserve. There is basically no need for a 64-bit kernel for our regular Mac single user workstations & laptops.

To add to what Nigel said, neither FCS nor CS4 has been rewritten to use the 64-bit-capable Cocoa programming interface yet.

Adobe announced some time ago that an upcoming CS release would use 64-bit-capable Cocoa code, but it's not yet known if this will be ready for CS5 (coming out in a few weeks) or in a later update or release. It's a serious amount of learning curve for the programmers and over a million lines of code to rewrite, so it's not a trivial endeavour for either Adobe or Apple.

FCS is known to not support this natively at this time. Perhaps in FCP8? There's a lot of legacy code that Apple has to rewrite and test. As good as Randy Ubillos was, that's still some 10-ish years of legacy code to deal with.

Even without full 64-bit support by the applications, you are still capable of taking advantage of most of 64-bit's benefits today, so no great loss at this time for most people. I'm still annoyed that my 64-bit-capable MBP (with a 64-bit EFI) was blocked by Apple from booting into 64-bit mode, though. :-) Not the end of the world for me.