Great form factor, smooth operation in every circumstance I've deployed it (even against my thigh on a crowded train) and long battery life. Just about the perfect laptop mouse in my experience.Light, portable and hard-wearing. I've dropped mine many times with no damage or impairment of function.I lost my first one due to stupidity after nearly two years of use and three battery changes(!) and was so bereft I bought another that night even though it was the wrong color. I then used that one to order another red one. It is that useful a device.The buttons have a nice positive click, the wheel is the "clicking" sort I prefer with detents in scroll mode and has a tilt function for horizontal scrolling.And if you need to move it from machine to machine, you can store the tiny USB dongle inside the mouse so it doesn't get lost.A winner from Logitech.[EDIT 10/4/13] I started to see false double-click behavior last week and so swapped out my three+ year old M305 with the one I bought for a spare back in November of 2011, which returned sanity to my mouse usage.Three years plus from a mouse that cost me less than $20 and which has been toted around in some very hostile conditions isn't bad. I don't know what has broken, but it gave good service until it did.I would not want to pay the prices I'm seeing for this unit of late. True, the current "in stores" model does not have the nice hinged buttons of this one, but a portable mouse is always going to get a beating and should be either armor plated or disposably inexpensive as a consequence. I define this as about $20.All of the above In My Opinion, of course.[/EDIT][EDIT 3/19/14] The USB receiver went out on the replacement mouse after about 11 months usage. The price on these units has risen to the point I can't afford them any more so I bought a 325 to replace it. The 325 is almost identical in use (if not in look) but for the clickless mouse wheel, which I hate. YMMV. [/EDIT] 

Question: How is the button?
Answer: Great