From a recent press release:
Congress on Sept. 29 granted a reprieve to cruise passengers but not to air travelers. The amendment delays the implementation of the new passport requirements until June 1, 2009 for land crossings at the Mexico and Canada borders and for cruise passengers coming to the U.S. from the Caribbean, Mexico, Canada or Bermuda. Congress remained silent on the air portion of the WHTI, so the implementation date of Jan. 8, 2007 remains in place meaning any U.S. citizen entering or returning by air to the U.S. on or after that date needs a valid passport. In simplest terms, travelers to the U.S. by land and sea will need a valid passport by June 2009, 20 months away. Those traveling by air will need a passport by Jan. 8, 2007, two months from now.
For passport details, visit www.travel.state.gov/passport/get/get_840.html