Apple’s Mighty Mouse is not so mighty after all. After some time, dirt will fill up the scrollwheel and you cannot scroll anymore. I did some cleaning by rubbing the wheel over a tissue with some cleaning fluids, but that didn’t work anymore after half a year.
I found this tutorial on the internet that tells you how to take apart your mouse and clean it good. It’s not for the faint of heart, and you will definitely make some scratches on the bottom ring, but you hardly see it after you put it back together. I didn’t use a chisel, but used a small house knive (use at your own risk).
Here are the complete instructions: