The great experiment in discovering exactly what are the parameters of anonymous flying in these here United States continues. This Wired story by Ryan Singel, an eyewitness and facilitator to the drama, tells of how Jim Harper, a member of the Department of Homeland Security's privacy advisory commission (and participant in a 2005 Reason debate on airline security issues), did succeed in flying out of San Francisco airport without an official state I.D. In fact, his gambit resulted in a much quicker move through security than merely lining up with the branded peons--read the whole story.
For guidance to Reason's voluminous past writings on the issues surrounding flying, security, and I.D., see this March Hit and Run post, containing within it many other links to follow, all duly signed by their actual authors, drivers licenses available upon request.
UPDATE: Of course, the not-showing-I.D. thing doesn't work out that well for everyone, as see this recent account from travel journalist Edward Hasbrouck, who ended up talking to cops at Dulles for daring to ask questions about the precise responsibilities and powers involved in showing I.D.s at airport checkpoints. Hat tip to our man Charles Oliver.