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.