My system:
AMD Athlon 64, 2000 MHz 3200+
MSI K8N Neo4-FI/Paltinum
nVIDIA nForce4 Ultra, AMD Hammer
NVIDIA GeForce 6600 (256 MB)

Booting with -force64 indeed makes system work in 64 bits. Activity Monitor shows all programs working in 64 bits. 32 bits VLC player doesn't work, 64 bits works. Quicktime X in 64 bits doesn't work, shows endless "loading movie". Forcing programs to work in 32 bits mode through "Get info" doesn't work. Programs crash. So it seems like every program must be in 64 bits mode, or 32 bits. it is conrtary to the screen shot of Activity Monitor that I've seen where it was obvious that some programs run in 32 bits and some in 64 bits.

Kext Utility doesn't work in 64 bits mode.

And I still need OpenHaltRestart kext.