Whilst testing a game today, I noticed something odd. It seems that OS X actually has mouse acceleration built-in to the OS (I tend to use a Wacom for non-gaming tasks, so I hadn’t noticed this sooner).
The scourge of PC gamers everywhere for the past few years, the idea behind mouse acceleration is that it compensates for larger screen real estate by moving the mouse further when you move it faster. It’s not much of an annoyance when using the OS, but when gaming it can get annoying fast, particularly for first-person shooters. That said, many games seem to use their own mouse drivers and so it isn’t a problem.
The other unusual thing about OS X’s mouse acceleration is that there’s no visible way to change it. However, this post at OSXDaily provides a few ways to disable it.