I handle a lot of mice in this job (right now I’m using the Mionix Naos 5000) and I have to say that if a mouse were, like the Magic Mouse, shaped completely wrong for human hands, I would throw it away and never speak of it again. Others, while perhaps more crafty, are far less principled, and will go so far as to fabricate a silicone crutch to rest their hand on. There, I fixed it!
Now, if you can’t live without the few multi-touch gestures you can do on the Magic Mouse, this thing is probably a good idea, and it’ll set you back $10 (free shipping or $3 if you’re out of the States). But if the idea of using a device that was clearly not designed with ergonomic principles seems silly to you, as it does to me, then pick up one of the many great mice that are supported or semi-supported on OS X. I understand the Logitech MX Revolution is excellent, and many of Razer’s mice are supported as well.