With all the Magic Mouse nay-saying, I'd just like to add my voice to the mix to say that I've been using one for about three years now, and I absolutely love it. I cringe at the thought of using a normal mouse now, for the flexibility and customizability (especially when paired with the epic BetterTouchTool), smoothness and subtlety of scrolling, and (this is a big one) the fact that there is no gunk-prone mechanism on top of my mouse that requires cleaning frequently (before the Magic Mouse, the Mighty Mouse was my daily weapon of choice, and that tiny ball gunked up all the time (with dust, hair, whatever) and would become unresponsive, causing relatively frequent interruptions *at least every few weeks, if memory serves, and sometimes more frequent). Even with other mice that didn't seem to have the gunking problem, the scroll wheels were either too tense, or too lose (or worse they scrolled in little clicky increments... I hate that), whereas the sensitivity of the Magic Mouse feels so much more natural.
Never has it caused me any pain/strain/etc. Yes, it felt different than I was used to for about a day, and after that I was completely used to it and never thought about it again.
As for the fact that it's flat while your hands are curved unless you feel compelled to force your hand onto the shape of whatever mouse you're using (i.e. unnaturally force your hand to go completely flat over the mouse), I don't see how the shape of the mouse is terribly relevant. When I use mine, my hand is in exactly the same position as when my hands are resting on the keyboard: palm flat on the desk, fingers comfortably and naturally arched with the tips of my index and middle fingers resting on the top of the mouse. It is not some apocalyptically abysmal form factor, as many people paint it. Having extra bulk under my hand on a larger mouse now seems slightly uncomfortable.
Of course, there are all kinds of different hand sizes and shapes (mine are relatively large, I suppose, whatever difference that makes), and I imagine there are probably people out there for whom the Magic Mouse might actually be problematic somehow, but I kind of suspect a lot of this blowback comes from people who are change averse or just don't feel any need for a touch mouse (that's fine! Now just don't ruin it for the rest of us), or perhaps have tried it for a few seconds in the store and found it too different without giving it a real chance (in the first few minutes I considered returning mine, but again, after using it for just a short while, I loved it).
Bottom line: if you're happy with your mouse, more power to ya! But all this drama over a mouseas if this design is a deliberate attack on all creatures with fingersleaves me truly dumbfounded. You would think the thing was covered in razor blades the way some people complain...
