I use the MX900... 10x better than the Microsoft Bluetooth, however nowhere near the battery life of my Microsoft RF.
Then again, it has a little light that lets you know when the battery is getting low. Takes 30 sec to pop battery's in a charger. Also, I use the Duracell rechargables and they last a few hours longer than the ones that come with the mouse.
P.S. After using an internal bluetooth wireless mouse, I will never own a mouse with a dongle. It saves a ton of time in aggregate by not needing to plug/unplug, and I've ruined about 4 notebook USB ports due to playing games with notebook on my lap and crunching the dongle sitting in the now broken USB connector.