I took a good fall while skinning up a steep slope three years ago. Jerked my right shoulder real hard while stopping and it sure did hurt.
Since then, I'm highly prone to aggravate it when I play basketball, especially rebounding and dunking. Quick, jerky motions are bad.
It seems to do a lot better when I do military presses and other shoulder workouts.
Climbing doesn't bother it, unless I try to pull on it with my arm above and behind my head. Falling on it in a bad way can really tweak it, though.