I'm one of those who cracks everything... either on purpose or accidentally.

At most recent count, my neck, shoulder, clavicle, wrists, back, hip, knees, feet and toes crack. The only ones I do on purpose are my neck and my back. Everything else just happens whenever.

I do have to crack my back every morning before I get out of bed though, otherwise I have trouble moving. In my case, it's because the cartilage is wearing away... but it really freaks people out!