Matt: I agree that accepting a bump is a good idea, if you have the time to spare. Without a bump, I was once moved from DL to US because DL cancelled a flight. Not only did I stay in the front cabin (I'd been upgraded on DL), but I also got miles on BOTH carriers. Do you think this would also work if you changed carriers because of over-booking?

yes philforest - it works too.

philforest, this also applies if you volunteer in case of overbooking and the airline routes you to another carrier.

In addition with United if they ask for volunteers but then do not bump you, they will give you a $25 certificate. With Northwest, if they bump you they will give you a certificate which can be used to get 500 miles.