Best not to use the term "deported" since that is a specific legal and official procedure that wouldn't happen here. What would probably happen to BallardFlyer at the Immigration counter is he'd be taken aside to an airport detention room and questioned, then fined, and likely blackballed electronically and with his passport marked with the dread red "X" over the TWOV stamp he received in his passport when he arrived. Expect to have difficulty in the future with getting a Chinese visa, at least with that passport.

Ballard, I strongly advise you not to pull this stunt. The cost of the visa, even for a US passport holder, is less than the cost of a two-day fine. Another issue: Where would you plan to be staying overnight once past the 72 hour limit? No hotel or hostel will accept you if it means you'll be over your legal stay limit as marked in your passport.