i jumped off of a lift once, but it was only from about 10 feet in the air. my homie unclicked my ski with his pole, so my ski went tumbling down right under the lift - like I said, we were only about 10 feet in the air and only about 15 feet up the hill, so I just bailed off of the lift to go grab my ski. The lift op laughed. There was no one else on the lift aside from my asshole friend, so there were no concerns with anyone getting hurt.
I generally do not condone jumping off of lifts though. Realistically, chances are slim that a chair will derail, but it's still not worth the risk. It'd suck to be responsible for some fuckin' gomer falling off of the bouncing chair because you decided that it'd be cool to jump. Especially if said gomer decided to sue the shit out of you and or your hill because of it.