I just got off a US Air flight from Charlotte to Raleigh after a business trip to Wyoming. My seatmate was a very nice woman who regaled me with the story of how, on her earlier flight on Cape Air from Cape Girardeau, Missouri, into Saint Louis (the country's 31st-busiest airport), the pilot allowed her to sit in the co-pilot's seat, from takeoff clear on through to landing. (Here's Cape Air's route map.)
It was a small plane, she explained -- a nine-seater--and she was one of just 3 passengers. Cape Air says its fleet includes "two ATR-42s and fifty-six Cessna 402s," so I'm guessing it was a Cessna 402.
As the 3 boarded the plane (the other two were "kids," she said), the pilot asked them whether one of them wanted to fly in the cockpit with him. The other two declined; she said yes.
She sat just next to the pilot, with full access to him and all of the controls throughout the flight. He schmoozed with her when he wasn't talking on his headset to control, she said. He said he'd flown commercial jets for Continental Airlines until he was laid off fairly recently and took the job with Cape Air.
I am not making this up, and I have no reason to suspect that she was either.