Jennifer Granick and her student Jessica Hubley have written a fantastic response to TSA.
The money quote, IMHO, is:
"Our client is in the business of studying security. He is neither the first nor the only individual to criticize flaws in the TSA’s security procedures nor the only person to describe flaws in the way that boarding passes are created and used. He should not be subjected to civil penalties because he did not violate the Federal Regulations cited in the TSA’s letter, because the regulations cannot be enforced against him or other passengers, because the civil damages provision cited in the TSA’s letter does not apply to the cited regulations, and because Mr. Soghoian’s website is protected by the First Amendment."
I'm posting the letter here (see below).
If you'd rather view a pdf offline, you can find one here.