My old MX1000 which I've had for almost two years now started having some strange issues with the scroll wheel. It got really stiff and wouldn't scroll down anymore (scrolling up was fine!) The battery life on the MX1000 also went down the hole so I called Logitech and without much hassle they shipped me out a new mouse. The MX1000 is discontinued now so they sent a MX Revolution instead, which is fine by me.
It came in last week and so far I like it a lot more than the MX1000. The grip is a lot skinnier than the MX1000 and as a result is much easier to hold. The MX Revo has fewer buttons (no quick scroll up and down), but those never worked for me in my dual screen set-up anyway. 
The really cool part about the MX Revo is its scroll wheel. It has two modes: regular boring scroll wheel, and an incredible free spinning mode 
In free spin mode you can flick the scroll wheel and it spins.. forever! It makes navigating through long documents or web pages much faster.
So oddly enough, my MX 1000's scroll wheel seized up and my new mouse has a free spinning wheel. As for battery life, I've tested it this week and the mouse lasts a lot longer per charge. I've only charged it once so far and I have been able to use it for ~4 days with pretty heavy usage. The MX1000 was dying after half a day. 
Overall I'm pretty happy with the replacement. Compared to Microsoft's hardware replacement, shipping was slow as balls, but it got here so no complaints. 