From the looks of Steve's e-mail, I'd say it's slim to none. Steve thinks it's a non-issue....A revision in both design and the manufacturing is a very costly procedure that would cost Apple millions. Don't think a CEO as on top of the ball as SJ would do something like that when they didn't have to.
It's going to be very costly when people start returning them due to poor signals. Do you really think a Genius is going to say this to someone's face: "Well, sir, you're not holding your phone right. You should really be holding it this way...". Good luck with that spin.