The U.S. Department of State issued a Worldwide Travel Alert on Friday, which news outlets have now found to be because of possible terrorist action specifically in the Middle East.

The alert states:
"Terrorists may elect to use a variety of means and weapons and target both official and private interests. U.S. citizens are reminded of the potential for terrorists to attack public transportation systems and other tourist infrastructure. Terrorists have targeted and attacked subway and rail systems, as well as aviation and maritime services. U.S. citizens should take every precaution to be aware of their surroundings and to adopt appropriate safety measures to protect themselves when traveling...
We recommend U.S. citizens register their travel plans with the Consular Section of the U.S. Embassy through the State Department's travel registration website. We strongly recommend that U.S. citizens Traveling abroad enroll in the Department of State's Smart Traveler Enrollment Program (STEP). STEP enrollment gives you the latest security updates, and makes it easier for the U.S. embassy or nearest U.S. consulate to contact you in an emergency. If you don't have Internet access, enroll directly with the nearest U.S. embassy or consulate."

Up to date information can be found by calling 1-888-407-4747 toll-free in the United States and Canada or, from other countries, on a regular toll line at 1-202-501-4444. These numbers are available from 8:00 am to 8:00 pm Monday through Friday, Eastern Time (except U.S. federal holidays).

Update: Yemen embassies were evacuated (including a friend of mine who works there as a diplomat). Her group at least is safe in Germany. Now, the proverbial crap is hitting the fan in Pakistan. (hey, that rhymed)