I hate the crappy Windows mouse, which is designed for righthanded people, forcing a lefthanded person to have to figure out how to reverse the buttons. As usual, the single button mac mouse is highly effective and simpler to use. (My mac-expert friend looked at me in justified puzzlement when I first got my imac and asked how to change it from right to lefthanded.)
And why wouldn't you go into Control Pannel -> Mouse and switch the buttons?