I got this mouse after my aging wired mouse started making weird clicking noises and I grew tired of cleaning out the ball of my trackball. Phew.
Review of the Logitech Nano mouse
So far I love everything about it. It has a lot of buttons which suits me perfectly: the more buttons the less I have to use modifier keys or point at a specific part of the screen to get the "back" button.
The USB receiver is so absolutely teeny tiny that it is easy to forget you even have it plugged in (aside from the fact that it takes up a spot in the USB receiver). Glorious.
I've had a pair of these for 4 years now. After extensive use (basically every working day for at least 4 hours and frequently taking them on/off) the plastic cracked at the point where I fold them around my ears. Bummer. But, for this kind of (ab)use it's not all that surprising.