let's start with an example: persoally i would prefer to have

 - double-click left -> open folder
 - single-click middle -> open & close folder

i realize that this is probably not what most people want to use but it
would be very handy for me. i think that usage of the mouse buttons should
be more configurable so taht anyone can adjust it to the way she/he likes
it. mouse button mapping (what button does what) and configuration (things
like single/double click) should be added to the "mouse preferences" dialog.