It works fine, but it's awkward to use, the strobing of the sensor LED can be annoying, and it has exceptionally low DPI. It's also very easy to try to click and end up shutting the mouse off by flattening it. It's certainly a $70 gadget, but is bested by even the cheapest 'normal' optical mice as far as being a nice input device.
To be fair, its owner really likes it. For me, though, it was the first time I actually preferred the glidepoint to a mouse.