From the website of the US State Department
With the exception of the passports of American professional reporters or journalists on assignment in Iraq, and Americans residing in Iraq as of February 8, 1991, U.S. passports are not valid for travel to, in or through Iraq, unless they are validated by the Department of State.
You can get a lot of good information about traveling to foreign countries, as well as safety threats when you're there, by looking at the Travel Warnings and Consular Information Sheets available at http://travel.state.gov
. For example, the current Iraqi information sheet informs us that it is not uncommon for the government of Iraq to use foreign visitors as a human shield against coalition enforcement of the no-fly zones.