Most (good) Mac applications are designed to be used with a one-button mouse. In the Mac OS, for example, there is functionality for multi-button mice, but all features can be accessed with a combination of the keyboard and primary (left) button. This is why apple mice before the mighty-mouse have all been one button, and why the apple laptops continue to ship with only one button.
I'm playing UFOAI on my MacBook, which means I can't turn a soldier without taking a step- a serious disadvantage in this game. (I do have a mighty-mouse, but I'd rather not require it to play.)