Here's a great tip from Consumerist: airlines' cargo-tracking websites often give the real explanation for flight delays on their passenger jets. The next time your flight gets delayed, try looking up the story on the airline's cargo site and see if the problem is the airline's fault (mechanical failures and so on), and then use that as evidence to get refunds/miles/tickets out of the airline.
It can be hard to get a straight answer out of airlines sometime about the real reason a flight is delayed. For some reason, though, they're more straight up about their packages than their passengers. See, the airlines have special cargo websites which are supposed to be for people tracking packages they're shipping through the airline. Here's the cargo sites for some of the major carriers...Link