I am an extremely happy Evoluent customer. The mouse is absolutely terrific, very comfortable and actually _more_ intuitive than a flat mouse once you get used to it. With the exception of my graphics designer, every single person in the office fell in love with my vertical mouse when I let them try it for a few days.
However, nobody is willing to pay $100 for the mouse, just like they are not willing to pay $70 for a mechanical keyboard. I think that people see cheap mice and keyboards for $10, so they feel cheated when they spend much more than that on peripheral equipment. The truth is that I'm a sucker as well. Even though I have an Evoluent at work I still use a flat mouse at home as the price of a second Evoluent is hard to justify to myself when I hardly use the mouse at all (Vimperator, Linux).
Damn the price, trust me, you want that mouse though. The discrete middle-mouse button is only the icing on the cake. Almost _everything_ on that mouse is absolutely terrific.