Privacy.org: "The Department of Homeland Security's Transportation Security Administration Agency (TSA) disclosed that it amassed a secret database of air travelers who arrived at airports without a drivers license or passport. The database also includes information on the traveler's companions."
The collection of names into an official List is always cause for concern. While many people feel these things are created without much purpose, this is almost always not the case: the purpose is to remember who was where, and under what conditions. So they can decide what to do with you... later.