I bought this mouse as a replacement for the Apple Magic Mouse, which I find gives me hand cramp after prolonged use due to its very flat shape. This mouse, although very light, is much more ergonomically shaped, allowing you to rest your whole palm on its surface - much more comfortable than the Apple mouse (and yes, it works with OS X and Windows).
However, from the product images you would expect this to be a crisp white colour, when in fact it's closer to the off-white greyish colour of computers from the 90s. Just worth mentioning if anyone is buying this on looks.
But apart from its appearance, which doesn't really matter a great deal, this mouse is responsive and easy to use, and at this price, you won't find a better mouse. I'd tried using similarly priced laptop mini mice, and this is just so much better.
EDIT 11/11/2012 I should mention that after a while using this mouse for video editing, I have started to find it a little too light - even with sensitivity set to minimum, the cursor feels like it pings around the screen a little too fast due to the fact that the slightest knock will move the mouse. I found that blue-tacking a few 2p pieces to the bottom added a bit of extra weight and made the mouse feel a bit more precise. For this price you shouldn't expect the precision needed to editing/gaming, so tweaks like this might do the trick for budget-wary power users.