MSN Travel has a good online article about passport usage, passport protection, and the new  laws that require a passport for almost any type of travel that takes you out of the United States. The article begins:

At first glance, a U.S. passport is just a little booklet, about the size of a pocket notebook, a slim binding of heavy, baby-blue paper. But with this tiny document, you can visit almost any nation on Earth, earning approving nods from customs officials and collecting exotic stamps, one border post at a time. With a few notable exceptions–such as Cuba and North Korea–a U.S. passport is respected in almost every harbor and airport on the globe.

And recently, with the tightening of Homeland Security, your passport isn’t just a ticket to places–it’s your ticket back. If you’re finally taking that romantic trip toEurope or you’ve bought tickets for an Asian adventure, your passport is mandatory for travel to most foreign countries. And beginning on Jan. 23, 2007, the document will become even more essential for zipping around North America. The Western Hemisphere Travel Initiative will require that anyone who takes a flight to Canada, Mexico or the Caribbean must have a passport or other approved identity card.