After the last time my Ubuntu 10.04 installed updates, my mouse middle button stopped working. The mouse is Toshiba and has three buttons (the middle one below the wheel). I activated the emulation in the meanwhile, but I prefer to keep using the button. I really don't know what update ruined it. Now I have kernel 2.6.32-43-generic.
The only configuration file I found is: /usr/lib/X11/xorg.conf.d/05-evdev.conf