They began production of the U.S. Passport Card in July 2008. They’ve issued a lot of cards and it takes about 4 weeks to process it. It’s s wallet sized passport card that is less expensive than the regular passport. The problem is that it can’t be used for international air travel. It can only be used to enter the US from Canada, Mexico, the Caribbean, and Bermuda by land or sea but not by air.

The people that it works best for are those who live in a state that borders on Canada and Mexico so that they can frequent those countries by land/vehicle. You can get more information here.