As I mentioend in a previous thread, I'm thinking of replacing my dead MB with a MBP. Would the early 2011 (2.3 GHz Dual Core i5) MBP be 32-bit or 64-bit (like my Quad Core iMac?). Just curious.
As was said above, OSX will run any x64 apps that you have for OSX, but you can force the machine to always boot in 64 bit, which will run all apps as 64 bit unless they are incapable.
All Macs that have a Core2 series or i-Series processor (in other words, all Intel Macs except the first generation of most of the models) can run 64-bit apps. Booting the 64-bit kernel is generally unnecessary, but can be done by most recent Macs.