A trusted friend of mine flew out of San Francisco on a domestic United Airlines flight yesterday.
He realized earlier in the day that he had forgotten his wallet, and emailed me for advice/info. I sent him a pointer to the Appeals Court ruling in Gilmore vs. Gonzales, as well as a few news articles that tell you what to say at the airport.
He said he didn't have a single problem. The United check-in employee didn't bat an eyelid when he was told that my pal didn't have a single piece of ID. The employee typed in a few keystrokes on his computer, and out came a special SSSS boarding pass.
Likewise, at the TSA checkpoint, the person checking his pass shouted "secondary" and then let him bypass the entire security line. He was also able to successfully (and without any pushback from TSA) decline to go through the evil puffer machine, and instead opt for a hand pat down.
Total time to go through security: Less than 10 mins.
The knowledge that you were able to fly without presenting your papers: Priceless.