Another great way to milk the bump game is to watch the departure board to see which flight out of a hub has cancelled, and then call and purchase a fully refundable ticket on the next flight on that route.

9 times out of 10, the folks from the cancellation will cause the next flight to be oversold since they are already at the airport they won't be no-shows, but there isn't enough time to change the overbooking profile accordingly. On the rare occasion that it isn't, you refund your ticket and go home.