Dodgy mouse mappings

So you're trying to use (say) your middle mouse button to copy/paste and the darn thing isn't working.... Well there's a bunch of things that control this (see a some articles here, and uhere, khere). Basically if you want paste working with a particular mouse button then you need to make sure it is the second one (ie button two) in the list; So for a normal 3 button mouse the mouse maps (see below) should read: 1 2 3 .... But for ,say a Logitech Trackball, the mapping may want to look like this: 1 8 3 4 .... (as the small left button on these trackball's is actually numbered 8 - check using xinput query-state your_mouse_id).

• List your input devices using:
  
  

  xinput list 

  List mappings using your mouse's 'id' (from xinput list):
  
  

  xinput get-button-map your_mouse_id

• The X config file: /etc/X11/xorg.conf file at the InputDevice section
• The xmodmap set-up - have you got a .Xmodmap or .modmaprc file lurking? Check your existing setting like this:
  

  xmodmap -pp

• The HAL policy - see /etc/hal/fdi/policy/ - any special config there? (NB: HAL disappears from Ubuntu after Karmic 9.10)
• The UDEV rules - see /etc/udev/rules.d/ and/or /lib/udev/rules.d/

[updated:17jun10]