Microsoft's got a new mouse, the Microsoft Arc Touch Mouse. Here's a video of its designer Young Kim introducing it:
Now, let's philosophize about it the Xah Way. First of all, it's a portal mouse. That means, it's not the most comfortable, ergonomic, mouse. It's not for professional heavy-duty 8-hours-per-day gaming, 3D modeling, image editing.
Being a portable mouse, its attraction is limited, because, if you are on the go, you may not need a mouse at all. For example: ① You don't carry a mouse at all. The trackpad does fine for the occasional 1 or 2 hours use of a computer. ② These days, many will do fine with a tablet computer such as iPad amazon. With a tablet, you just touch the screen, you don't need a mouse at all. ③ For those programers on the go, tablet is out, but then, programers don't need to use the mouse that much.
So, now for the few who really like to have a mouse for the go, i suppose this is fine. Not sure the space-saving matters that much. As far as ergonomic and efficiency goes, it couldn't be worse than Apple's input devices.