The Post is reporting today that the MTA has begun modifying the subway system's turnstiles so that they will no longer give free rides to those who know how to bend their expired MetroCards in a particular way. As that group of people includes myself, and occasionally a bent MetroCard is my only ticket home from the bar, I am understandably sad that an era of quasi-legal free transit is over.
It'll take them a while to finalize their testing though, so we may very well have a few more free rides left during this period of twilight. I recommend bending the magnetic strip on your expired MetroCards a little over three-quarters of an inch from the right-most edge (between the C and the A in Card). Swipe 3 times, and on your 4th swipe you should be let through (if you've done it right).
If the above instructions fail you, and they likely will (it takes practice), you can learn the way I did. Just start picking up as many bent cards as you can, eventually you'll see the consistencies.