Friendly gate agents can move heaven and earth if motivated. I was on a flight from FLL to DFW with a coworker. His wife decided to join us on the trip at the last minute. After a pleasant chat with the gate agent, both were upgraded with me and they even extended their upgrade on the following segment I wasn't flying!

Moral of the story: Be pleasant and let them enjoy the time talking with you. Friends help friends in my theory. Those that scream and yell and threathen should be assigned seats in the rear of the plane and last to board (yes, I do have a nasty side).