This is the JSCO Optical Noiseless Mouse; it has been designed to be as quiet as possible. This alone is an unusual feature for a mouse, in fact until now there was only 1 other 'Noiseless' mouse available to buy. This mouse has been designed in Korea and is only available via import.
Now I don't know about you but having grown up with modern technology readily available, I am quite use to the comforting click of a mouse, just like you expect a keyboard to make a small tap with every key press. This is why when touch screen phones came out they added vibrations to give you some form of tactile feedback as this is what people expect and are now used to. With some peripherals, especially keyboards, you need the feedback to be there or else it's nearly impossible to type at speed. Your fingers don't bounce off the keys and end up resting on the key creating all sorts of mistakes. That being said with the recently released iPad it is quite possible to overcome this and get used to not having any feedback to the extent that with a bit of practice touch typing at a decent speed is achievable. A mouse that doesn't click by principal seems a slightly weird concept to me but one that mirrors the technological advances taking place with all sorts of devices.