You'd be forgiven for thinking Microsoft's Arc was the latest exercise in design wankery, as we certainly did when images first started filtering down. Thankfully however, this is completely untrue. The Arc is a case of form following function, and not the other way around — as the space under the mouse serves as an area for the rear end of the mouse to fold under, cutting down the size dramatically when it comes to storage.
This effectively gives the user a notebook-sized mouse when they want to pack it away, but a full-sized mouse when they're using it, avoiding "the claw" that so many notebook users have to employ to use the tiny mice. The hinge is strong too, and so won't break in a hurry.
While the wireless receiver is small, it's not quite the size of Logitech's tiny receivers, and we wouldn't feel safe leaving it plugged into the laptop while travelling. Thankfully, it handily locks to the underside of the mouse magnetically when you want to stow it away, meaning it's quite hard to lose. The mouse takes two AA batteries to power, but is still a comfortable weight.
Aside from the usual two buttons and middle button/scroll wheel, there's a thumb button on the left-hand side — other than this the mouse is symmetrical, making it mostly suitable for left and right handers.