Comment 7 for bug 96600

I had the same problem yesterday, and I still have it, but I discovered a way to fix it temporarily.
Believe it or not, the problem has nothing to do with the nvidia driver (at least in my case it doesn't)

I discovered that when you use the evdev device, the Event number for your device could change every time you reboot.
What you need to do is look for the new event number for your device:

cat /proc/bus/input/devices

and then edit your xorg.conf accordingly, to reflect the new number.

There's a way to force the system to use the same event number for a specific device.
If you do a search you may find it; I'll look for it later when I have more time, and id I find it, I'll point you to it or post it here.
Please do the same if you find the solution.