You're mixing up two concepts. By "booted 64-bit", you mean running a 64-bit kernel. It doesn't matter if you're running the 32-bit or 64-bit kernel from a us

You're mixing up two concepts. By "booted 64-bit", you mean running a 64-bit kernel. It doesn't matter if you're running the 32-bit or 64-bit kernel from a userspace app's point of view - 32-bit and 64-bit userspace apps can run on either kernel. All Apple's apps that ship with Snow Leopard are 64-bit (Safari included). A 64-bit Flash would run in 64-bit on all Intel 64-bit capable systems regardless of kernel - reducing memory footprint, because the 32-bit frameworks, currently loaded to service 32-bit Flash* would not need to be loaded into RAM any more. If you're interested in which userspace apps you run are 32-bit vs 64-bit, Activity Monitor has a "Kind" column - or in 'top' in the terminal, the 32-bit apps will have a '-' before their name. The 'extensions' you refer to are kernel extensions. By default, Snow Leopard still runs, on all systems, with a 32-bit kernel. A 64-bit kernel is available (and will presumably be the default in the future), but most third-party kernel extensions are shipped only in 32-bit form. Unlike userspace apps, 32-bit kernel extensions can't be run in the 64-bit kernel, so Apple still uses the 32-bit kernel by default so that people's kernel extensions will still work. * and iTunes if you're running it, but that's another story...