You will limit your options if you exclude all mice that have USB dongles. As I said earlier the VX Nano has three additional buttons that can be programmed in addition to the fantastic scroll wheel that it uses. It's significantly better than the Mighty Mouse and I would easily buy this one again should I lose it. I'm not worried about the dongle since it stays in my machine.
I ordered the Mighty Mouse when I purchased my MBP back in Feb 2008. Battery life is pretty good since I haven't replaced my battery since just now (a coincidence?). Like others have said, if you clean the scroll ball on a regular basis, you should be fine. I clean mine with a sanitizing wipe and turn the MM up side down to clean the ball.
The MM doesn't have a Back/Forward button and coming from Windows, I was used to that. But I have gotten used to it. Whichever mouse you are going to get, don't get the one with the USB dongle. Your mouse would become useless if you lose the dongle, and why carry an extra piece when you can do it without (BT). Good luck.