Bought two of these 6+ months ago, one for work, one for home.
Pro: Great mouse, coolest mousewheel so far. Great precision. Wireless, great range, tiny usb receiver. Feels great in hand (I got large palms). Battery indicator idea is great. Charges fast.
Con: Construction is somewhat shoddy on the electronics part, the one at work has a now busted battery light indicator. The software driver for WinXP is crappy, known as bloatware. Too large and too buggy to be useful, plus the bi-monhtly updates involve downloading 20MB+ files. Very disruptive. The little search icon silkscreened on the top middle button scratched off in like 2 weeks. Nobody is missing it, though. Also a drawback of wireless is that sometimes you forget to charge it and it runs low at the worst times. It's not fair to blame that on Logitech, but come on, they could make it crawl back to base and recharge, right? Right ;-)
Anyway, overall, it's great, would buy another one.