3 and 4 finger swipe stops working on MBP 13"

"What happens when you go back to 32-bit kernel?

OS X is different from windows, in that the OS Kernel can run 32-bit and still support 64-bit applications and address more than 4GB of memory.

The problem with forcing SL to 64-bit mode (or rather why its not set by default) is that not all kexts (drivers) have been updated to run in 64-bit kernel.

Just a hunch."