I dont know of anyone that does. I wear boxers when I ride and i'm fine. Every so often you get a love tap from the seat or gas tank, but its not that bad. I dont think I would wear a cup because they are so uncomfortable, I didnt even wear one during football, and I didnt know of anyone that did.
I don't get to ride much, but I wear a cup every time. The newer style cup with compression shorts is much more comfortable and you get used to it really fast.
A guy I know lost one of his boys in a very minor collision, and he now wears a cup all of the time.
Once I am dressed in my gear, you can't even tell I am wearing a cup and I wouldn't ride without one.