Another thing to note on Jetblue's standby policy...while it is true that you can fly standy on the flight prior for free, it does NOT necessarily mean you will get the same nonstop flight and city pairs.
For example, I recently had a nonstop LGB to JFK flight. I wanted to get on the earlier nonstop flight, but was told that the flight directly before mine actually was considered to be LGB to AUS to JFK, which actually got me into JFK AFTER my original flight would have been. The only difference was that it took off from LGB (with a layover) before my original nonstop flight.
Needless to say I wasn't very happy about this policy, and the customer service agent wouldn't budge. Has anyone else had this happen to them? It seemed like a silly policy to me, so I wasn't sure if this was actually true.