Well, fair enough that you were exposed to them. I didn't have a lot of friends, especially not those even remotely into any kind of tech, as a kid; I think I first heard of trackballs from a programming teacher in about 1996 and bought one to try out of curiosity. Ever since then I've used one whenever it was an option.
I've even mostly used the same model. If you look in my comment history, you can see I recently mentioned that most of what I use is Kensington Orbits. I've tried other models, but they don't work for me.
The one PC gaming exception for me is Minecraft. In that game you have to right-click a lot (as I'm sure you know) and I guess I haven't developed the muscles for that because it makes my wrist very tired very quickly. Still, I play a lot of FPS games and have no problem holding the right click for zoom and such; only quick, repetitive right-clicking causes problems for me.
edit: To address your original comment, I have one friend who uses a trackball at work but a regular mouse for anything else. Other than that, I rarely meet anyone who has even heard of them, let alone used them, let alone consistently done so.
Interesting, thank you for the edification.