Well, I ended up not taking it. There said they were looking for a number of people, they even went up to $300 and a number of people were lined up as I scanned my boarding pass - my name was first on the volunteer list but I declined.
Then, I have no idea what happened. I saw each and every one of the 8 or so people waiting to be bumped, walk past me on the plane. They must not have needed them. They looked annoyed, and there was no luggage space, so all in all I guess I cane out on top. In a weird way...