I don't have a problem with the new middle mouse button that sits slightly below the scroll wheel. I don't think it's "too small", and I don't have to re-adjust my hand to use it any more than I have to re-adjust my hand to use the scroll wheel.

However, I could understand that when using software with frequent middle-mouse usage (very few of my day to day operations use middle mouse) it might be less convenient than a true three-button mouse.

On the other hand, having the scroll wheel's "click" be the middle mouse button is much worse for all the mice I've tried. The amount of force required to click down on the scroll wheel is always too much, and you end up rolling the wheel when you intended to just click. An example would be, if you have configured your browser so that middle-click is "open in new tab": If I tried to do that with most mice, I'd be scrolling off the desired link before the middle click even registered. So having the middle mouse button be a separate button is an improvement, in my opinion, even if the button's location is a hair awkward.

The ideal situation would be to have a proper three button mouse, with a full size middle button, and the scroll wheel placed slighly lower and inset into the middle button.