Granted, you have to have quick reflexes to realize your mistake in mid-mouseclick, but I thought I'd share nonetheless.
[robg adds: I was going to reply to the submitter that this was standard OS X behavior and not really hintable, but then I though about the number of users who are new to the platform who may not know about this. In the Mac OS, mouse events are sent on mouse up, not mouse down -- in other words, everything happens when you release the mouse button, not when you press it down. Like any good rule, of course, there are some annoying exceptions to this: iTunes' lists comes to mind, where the entries are selected as soon as you press the button down. I'm sure there are others, but for the most part, it's releasing the button that causes the action to occur, not pressing it. On Windows, the mouse-down action seems to initiate the action, leaving you no chance to cancel.]

