I recently updated my Debian unstable and found that as soon as X started up, my keyboard & mouse stopped functioning. The only workaround was to add
Option "AutoAddDevices" "False"
Option "AllowEmptyInput" "False"
The problem seemed to be related to the new evdev driver with a custom kernel. This replaces the xf86-input-keyboard and xf86-input-mouse drivers however to work the "Event Interface" must be enabled the kernel config file
Device Drivers-->Input device support-->Event Interface
This will result in /dev/input/event* and the mouse and keyboard will now work without the above mentioned hack.