I've been using this mouse for some 20 days now. So far it's working great. The laser technology is really nice, mouse works well and smooth on shiny polished table, where my old optical mouse would constantly jump around, so I don't need to use mouse mat any more. It slides very smoothly. It's comfortable, hand doesn't get tired even after using the mouse all day.
Seems like battery will hold for ever. Logitech software for adjusting mouse settings also has the Remaining Battery info. When I first turned on the mouse, it said "1045 days remaining." Now it's 1088.
The only drawback I can see right now is using the mouse wheel as a middle button. When pressing it, the wheel also scrolls just a tiny bit. This makes it difficult to middle-click on links that are somewhere on a page. For those who don't know, middle-click opens link in a new tab. I solved this by duplicating the hidden thumb button as a middle button, all that is done using the Logitech software which you'll need to download from their website. Other than that, all buttons work as expected, although maybe the Forward browser button might be a bit too far forward for my mid-sized hand. Not very important though, since I barely ever need to use it. The Back button is in a perfect spot.
It is taking a while to get used to the mouse though. With my previous one (and all public mice, when using university computers), I knew perfectly well how much I need to move it to reach a link on a page or something. With this one it's somehow difficult. The mouse acceleration and enhanced pointing options are difficult to predict, but without them mouse is a bit sluggish. But this is probably my personal problem, not a fault of the manufacturers.
After using the mouse for a while longer I noticed that the previous issue with mouse wheel has disappeared, it works perfectly. The problem with unpredictable mouse movement was solved by uninstalling the Logitech software, everything works fine now. Also, I still have a lot of battery life left, it looks like it will actually last me 3 years.