I am giving my paper with Jeff at the annual conference of the Society of Economic Dynamics in Montreal.   And I just found 5 dollars Canadian on the floor in a conference room.  At first, I thought it was a practical joke but no-one popped out of  a room and snapped a photo.  So, I guess it was not a setup.  In present company, my experience is consistent with the following joke:

An economics professor and a grad student are walking along the sidewalk, and the grad student spots a twenty dollar bill on the sidewalk. He says, “Hey professor, look, a twenty dollar bill.” The professor says, “Nonsense. If there were a twenty dollar bill on the street, someone would have picked it up already.” They walk past, and a little kid walking behind them pockets the bill.