I've only recently started taking the MX w/ me to work. Before I just used a wired Intellimouse at work and the MX only at home. But dang it, I like the MX so much, I don't want to use the Intellimouse anymore. So I've been pulling the batteries. It's a 20-25 min drive to/from work. I might just start to leave it be if I get an extra pair of batteries. In fact, I'm lazy, so I might just start leaving it anyway so I don't wear the battery door down.
Wooster, I haven't used the MS BT mouse, but before my MX900, I'd used Intellimouse Explorers exclusively since they first came out years ago. I was always leery of trying anything else since I liked them so much, but now that I've got the Logitech, I kick myself for ever having thought like that. Too bad you don't know anyone that's got one so you could test-drive it and see for yourself if it fits your personal tastes.