According to Esther Lin of Fightlinker.com, Blaine dropped by a gym in Southern California and received a blow to the midsection from the man with the massive biceps. The stunt was an homage to Blaine's role model, Harry Houdini, who died from a similar punch. Says Lin:

The rather physically fit Blaine claims he chose Kimbo because the fighter is one of the few people he fears. From my observation, it does not seem as if the magician is intimidated. Before the punch, Blaine does look visibly nervous. I won’t spoil the fun but there’s no illusion involved to this bit. David Blaine simply stands in the middle of the cage, lifts up his shirt to prove he’s not hiding any protective material, and asks Kimbo to punch him. And after? Kimbo is wowed by David Blaine’s resistance to his gut shot. Kimbo’s manager jokingly asks, “Hey, is this going to make Kimbo look weak?” I don’t think so. And I hope after this, Blaine checks in with a doctor.

Given that it happened more than a week ago, it's safe to say Blaine's OK.

A signed coin-bend effect was also part of the taping session. If we were crazy, then would we still call that "Superman?" We'll find out for sure tonight.