Alright folks, let's get something straight.
First of all, I'm very much against the erosion of our civil liberties under the Bush administration. However, the need to show ID before getting on an airplane is not a threat to your liberty.
Take this from a pilot: The person in charge of your airplane (the Captain) has every right and responsibility to have everyone on his flight accounted for. Yes, you can even be refused boarding just because he says you can't. If someone refused to show ID before getting on my flight, they don't board. Tough shit. Quit being a martyr and take your seat.
Law or no law, the airline has a right to know who is traveling on their airplanes. This also applies to trains, rental cars, etc. They are responsible for their assets, and you better believe that they're going to require some form of ID.