I bought one of these a few weeks ago - the usb receiver is tiny (ace for netbooks / laptops) and the mouse has a low profile (not too bulky for a netbook case) and is very responsive. In fact, I find it more responsive than my more expensive desktop mouse.
I'm on my first set of batteries so don't know how long they'll last - Play.com's description only states 'Long battery life'. Only niggle I have with the mouse, and it could be a unit specific problem, it didn't want to work with rechargeable batteries for some reason, have had to use non-rechargeable ones.
EDIT: The black version is temporarily out of stock, but other colours are available. I ordered a black one when it was out of stock a while ago and it took about a week to come back into stock.