brian hefele's untidy spaceBetterTouchTool is a free little utility that seems to get updated on a near-daily basis. It sits quietly in the menubar, and its only purpose is to expand the multitouch capabilities of Apple touchpads and, wonderfully, the Magic Mouse. That's not entirely accurate, I suppose - the capabilities are already there, but the drivers Apple provides are as limited as Apple mouse drivers have ever been. For instance, as everybody knows by now, Magic Mouse has no middle click. This was my main gripe against the mouse, but one that I've managed to live with for a while now. My common-use scenario for middle click is that of opening links in new tabs in Safari, rapidly queueing up a series of things that I will examine as time goes on. In lieu of a middle-click, there were two options - right-clicking and choosing 'open in new tab' from the contextual menu, or cmd-clicking a link. Neither is ideal - the former doesn't work from the Top Sites page, and the latter requires that I simultaneously be on keyboard and mouse, not always the case for casual browsing.
BetterTouchTool has improved a lot in the past couple of weeks. When I first installed it, it added a three-finger gesture which needed to be assigned to perform a keystroke. This was all kinds of useless. Three fingers on the Magic Mouse is an exercise in tedium. Also, it didn't get me middle-click, which was pretty much my only goal. The more recent versions, however, have added support for many more gestures, and the ability to use them to send mouse commands. My needs are simple - left click does left click, right click does right click, and a single finger tap does a middle click. I like the use of tap vs click here - as my main use is to open links in new tabs, the tap is weaker and less deliberate than the click which forces me to move away from where I am at that very moment. So far I have only had one accidental tap, which merely gave me a paste operation inside of Vim, no big deal. If this starts happening more frequently, there are a lot of adjustments to be made to help keep accidents from happening. Additionally, if I feel like getting more playful with my mouse, there are myriad other gestures that I can assign as I see fit.
Update! I neglected to mention that BetterTouchTool also lets you bump the tracking speed way up, allowing one to make the Magic Mouse (or whatever device) track faster. I was already pleased at how much quicker Magic Mouse was than Mighty Mouse, but it seems people still think it's too slow. I suppose I agree to an extent, as I have bumped mine up a bit since running BetterTouchTool.