Actually they have been available for some time. While they are not valid for air travel, they are valid for auto and ship transportation out of and into the U.S.
As a citizen of Washington State, I go to Canada now and then, as well as Mexico, and in the past year have done so by car and by ship. So I’m thinking that this could be useful for me, to be able to carry a “passport” in my wallet.
I’m ordering one and will write about the experience.
Update 5/17/09 – Seattle Times article
Information is available here:
Wikipedia article on U.S. Passport Cards