Yesterday, Amazon finally delivered the Magic Mouse that I had pre-ordered a couple weeks ago. (Since I was in the market for a Bluetooth mouse anyway, this seemed like a perfect excuse to pick one up...)
The final verdict is still out, but I figured I'd share my initial impressions. Obviously, the biggest feature the Magic Mouse adds is Multi-Touch, very much like the iPhone or iPod Touch. And I can confirm that this indeed works flawlessly. Flicking the finger up or down to scroll through windows is an amazing improvement over using a mouse wheel, let along a scroll bar. Momentum scrolling works just like on the iPhone, feels very intuitive, and adds a tangible touch to most applications.
I haven't gotten used to the two-finger sideways swipe yet, for example to navigate back and forward in the browser. It works well enough, but I'm used to using the keyboard to navigate back and forward or switch tabs, so I don't typically reach out for the mouse for this task. But if you usually do, it should come in handy.
I've never owned a Bluetooth mouse before and wasn't 100% sure what to expect, but I have no complaints at all about this. Pairing it with my Macbook was very easy, and it works just as well as a USB mouse, without any annoying cables. This is especially handy for me because I tend to frequently switch the mouse between my left and right hands to suppress RSI symptoms, and not having to deal with a cable definitely makes this easier.
Now for the things that are not that great:
Most importantly, the tracking is way too slow, almost to the point of not being usable at all. The acceleration is high enough, so when moving the mouse quickly it is possible to move it from one edge of the screen to the other without having to lift it. But this doesn't help for finer movements, such as selecting an item from a menu or a toolbar. Many people are complaining about this issue, but thankfully this article describes a workaround in form of a terminal command to change the scaling factor. You can also use the MouseZoom tool to accomplish the same thing using a convenient preference pane. It's old but works just fine in Snow Leopard.
I'm now running on the highest possible scaling setting, which is a major improvement over the standard configuration, though I might end up tuning things down a bit. Overall I've never been very happy with the mouse support in OSX. The acceleration curve just feels off to me -- it starts off too slow, then accelerates too quickly. This article describes this issue in detail, and I agree with it. It also describes some solutions, such as USB Overdrive and SteerMouse. I have bought and used SteerMouse in the past, and it worked pretty well for me then. It doesn't support the Magic Mouse yet, and according to the website they are currently evaluating whether to add this functionality. I'm not sure if any of these options are compatible with the Magic Mouse, which I'm sure requires its own driver to support the Multi-Touch functionality. I'll have to experiment with this...
The mouse button (a single button that is sensitive to where it's being touched and can therefore emulate left and right mouse buttons) works ok, but clicking requires a bit too much effort for my taste (my previous Logitech mouse was significantly more sensitive, requiring barely any pressure). In fact I find operations that require moving the mouse with the button pressed (such as when selecting several paragraphs of text in a document) somewhat difficult.
Last not least, I miss having a middle mouse button, mainly to open links in new browser tabs or copy & paste text in the terminal. I suppose I will have to get used to holding down the Command key instead. I wonder if the mouse surface is sensitive enough that it could differentiate between left, middle, and right clicks.
Moving the mouse over my wooden desk is fairly noisy. Unlike my Logitech mouse, which was quiet and smooth, the Magic Mouse almost feels like it's scraping the surface. I may end up getting a mouse pad for this reason, but this seems to defeat the purpose of the new and improved laser technology that works on any surface.
In terms of ergonomics it's not the best mouse in the world, but it's not horrible either. It's still too early to tell how well I adjust to it. We'll see in a few weeks...
In conclusion, the Magic Mouse is definitely a fascinating piece of technology, and I am excited about future iterations of this or similar products. I absolutely love the touch based interface of my iPhone, and the Magic Mouse does a good job at bringing some of this to the desktop. But it certainly has its share of flaws. Hopefully a driver update will resolve the slow tracking issue soon, but in the mean time the workaround described above will need to suffice. As for the other issues: If you can, I recommend you try out the mouse in the Apple Store first, to see how it feels for you.