Re: I have a 7 button mouse...
>99.9% of ... users didn't ... know what to use them for anyway.
Much the same can be said for the middle button of a three-button mouse. Sure, 100 linux monkeys will tell you that you're holding it wrong, and that there's a shit-ton of different things you can do with it (most depending on your use of the terminal... sigh!). But anyway, there's no standard use for the middle button. So, YTF?!
Similarly, the right button (on non-antipodean mice) is nothing special. At all. It does one thing: contextual menus. Wooot! Hot Damn! Like you couldn't engage the other half of your brain to pull on a finger, then another finger, and then press one of the modifier keys concentrated in the lower left and right corners of your keyboard to--well--modify the click you're making with the left button? Oh, that hand is too busy keeping time. Why didn't you say so? But, WTF...
The decomposability of a mouse click (mousedown+mouseup, as in HyperTalk) and consideration of time (duration and sequence, in particular, of the two sub-events) makes the second/right (contextual menu) button unnecessary--or, at least, not strictly necessary. Nice to have n buttons (if n<π) but you can get the same functionality out of a single-button mouse; a little software gives me a third way to invoke the contextual menu i.e. get the same result as using the button at the other end.
Love the trackball of the Mighty Mouse, BTW, but the side buttons ... definitely a puzzlement.