I've wanted one of these since I saw it on Steve Clayton's blog (twice). And now I have one - lucky me.
One of the reasons I'll use a big mouse (compared to the gosh-that's-tiny notebook style) is the magnify button on the side. Just as I usually don't want to get off the keyboard to use the mouse to, say, save my document, I don't want to get off the mouse and use the keyboard to zoom and stop zooming when I'm presenting. I had a nice Microsoft mouse a few years back but the magnify button wouldn't work with the beta of Vista I was using and I ended up letting someone else use that mouse. So I'm super happy that the magnify button on this mouse works just beautifully with Windows 7.