My mouse4 is auto-run, mouse3 I have unbound, and mouse5 I usually use for a push-to-talk key.
However, one of the great things about extra buttons is when you make macros, you can make it so they do different things on different clicks. i.e. if you wanted to have a macro that cast mangle when it's up, swipe if there's multiple mobs, lacerate if it's a single mob, and FFF if it's down, you can use a macro like:
Quote:
/cast [button:1] mangle; [button:2] swipe; [button: 4] lacerate; [button: 5] faerie fire feral
#showtooltip mangle
Then when you left-click the button on the action bar, you mangle (and the icon will be for mangle, showing the cooldown, etc), when you right click it will swipe, when hit the thumb button (the rear one if there's two on the left side) it will lacerate, and when you hit the last button it will cast FFF.
I used macros like that for blessings on paladins, stings on hunters, etc. In case you're wondering, if you have [button:3] on a macro like that (which is the scroll-wheel click) it will not make you auto-run.
Edited, Mar 10th 2008 9:11pm by skribs