Some of my colleague said the Apple pro mouse attached to my eMac is Zero mouse button. It is because they can't really see where the button is, by using their $100 mouse knowledge. The mouse with button should had some sort of "breaking line". Some of them should had a significantly different colour plastic plate to tell him "this is a mouse button". Moreover, in between 2 mouse buttons, a mouse should have a scroll wheel or something.
I am an one mouse button advocate because 1) mouse is an extension of your hand. 2) Contextual menu is evil and 3) I hate too many mouse buttons, say in Microsoft Mouse. I really know that a multi-button mouse should provide more functions, say linear scrolling of a webpage/document, right click to bring up a contextual menu or click the button z from the tail of the mouse to fire up dashboard. However, extensive use of these function triggered by mouse will 1) forget the beautiful GUI, 2) need some hard time to customize if you go to a computer lab with a mouse contained only zero mouse button or 2000 mouse buttons or 3) push you away from the keyboard which can be finished much faster by using short cut.
The Mighty Mouse newly released by Jobs' and Co is really a smart product. Despite the name is a little bit cheesy, Mighty Mouse can benefit the Windows switchers without upsetting the hardcore old Mac one mouse button advocate.
The eMac in my room have two users. User number one is Chainsaw Riot who is an one mouse button advocate. He perform nearly everything by clumsy mouse clicks and GUI as he is not fond with keyboard short-cut. User number two is Tiney who is a Windows switcher and adapted herself to multiple mouse button. I think I will buy a Mighty Mouse as this Zero mouse button looking mouse made both of us to work the same as before without changing the mouse-using experience. Plus, it is not that expensive at all. (Compared with the pro mouse previously with a 400 dollars price tag)