Seems very compact and easy to store, but I don't know how user-friendly really is...
"The new 2P Slim USB Optical Mouse is a laptop mouse that transforms itself in order to be easily stored yet easily used when traveling and working with a laptop. This 5mm thin, fine-looking ?piece of mouse?, fits inside the laptop memory card slot or a small pocket, and solves both the problem of always having dead batteries, and finding extra space for a bulky mouse in your laptop case."