Last I read was that portions of the software/utilities included in leopard have not been fully ported to 64bit. but the core kernel I think is or else how can it address more than 3 gb ram...
I guess everyone forgot Steve Jobs demonstration of a 4gb photo running in 32bit vs 64bit app in OSX at macworld 2007 and difference in rendering speeds...unless it was the reality distortion field messing with my mind..
the other question now is....does the apps come in 2 separate installers like windows for x86 and x64 ? Most 3rd party vendor software don't state whether they run in 64 bit mode or not...which I think alot them haven't ported over to 64bit yet... just wondering.