Just did the install last night, and had a permissions problem when editing the .plist. I changed permissions manually, made the edit, and then had to repair permissions to get the kexts to load properly.
Now the computer does boot without any errors or obvious problems, but USB does not work. System profile does not shows four hubs but no USB devices, although the keyboard and mouse still do work (after install of drivers to update 10.5.6.). I can't get an external DVD drive to connect, and there is no evidence of keyboard, mouse, or webcam in System profile.
Thanks for the help.