My wife and I once got $200 each on such a deal... and it was real money, not a voucher... AND they rushed us across the airport on a golf cart, to get us on another flight that left at almost exactly the same time. Only difference was that it was a bigger, fancier plane (with personal TV's) and the flight took longer because of a different routing.
We got to our destination an hour or so later, and $400 richer.