Summary: Very nice mouse (tracking with the blue optics is much better then my old one) but there is a big problem (for me anyway). You can't scroll left or right with the middle scroll wheel. I use Excel a lot and this is crucial for me. Oh well.
Excerpt: I have just written a review on another Microsoft mouse which I loved partly because of it being very big and therefore comfortable for my big hands. This mouse is the opposite. The whole idea of this mouse is that it is mobile/portable. To justify this, Microsoft decided to make the mouse small. Now I bought this online via eBay and therefore had no idea as to what the size actually was (I am too lazy to check the details on the page).
Pros: Battery (Power indicator, uses just one AA, lasts ages), Portable, Power - Saving Feature