http://www.tsa.gov/press/happenings/...uirements.shtm
Beginning Saturday, June 21, 2008 passengers that willfully refuse to provide identification at security checkpoint will be denied access to the secure area of airports. This change will apply exclusively to individuals that simply refuse to provide any identification or assist transportation security officers in ascertaining their identity.
I, however, was recently denied entry to the secure area of an airport because I declined to show ID.