TSA will increase security in response to the kinds of terrorist attacks that Al Qaeda operatives are most likely to launch. They'll specifically be on the lookout for a hastily arranged attackthe kind of operation that an Al Qaeda cell could stitch together in a few days. An unsophisticated attack means, by definition, an attack on the softest targets in an airport.
We've wrung our hands before about the staggeringly vulnerable lines in front of ticket counters and checkpoints, where a single terrorist with an automatic weapon or a suicide vest could kill hundreds. TSA knows that a terrorist won't bother navigating his way into the sterile area if he can commit mass murder just by walking into the airport.
So expect to see more attention paid to pre-screening areas, with TSA counting on normal checkpoints to stop armed terrorists from getting deep into airports. Outside the airport you may see car checkpoints, and you should duly give yourself a little extra time to get to the airport.
Inside you'll see more troops with rifles wandering around the ticket counters, and don't be surprised if you see the occasional traveler pulled aside after a dog takes an interest in the traveler's luggage. Obviously this is not the time to test whether you can sneak contraband through security.
Meanwhile the State Department has issued a global travel warning, alerting US citizens of the "enhanced potential for anti-American violence" and "strongly [urging them] to limit their travel outside of their homes and hotels and avoid mass gatherings and demonstrations." The warning also reviews basic safety precautions: make sure you're in contact with the nearest embassy or consulate, make sure you're signed up for emergency embassy updates, and make sure family and friends know where you're supposed to be in case you don't get there. Read up on all of that and more at State's travel page.