As I am local for this, I thought I would put up this latest news from this AM's paper regarding transportation connections from PHL during the Pope's visit whilst Philadelphia is effectively under martial law and shut down. The Regional train from the airport WILL now run at 30 minute intervals that Saturday and Sunday. However, there will be two stops only - University City, and Jefferson Station (aka 12th and Market). These are both in the "no-drive" zone, and will not do people a lot of good, if you need to get to 30th Street for any Amtrak train you will have to do this on foot. Tickets may only be bought outside TSA checkpoints for terminals A-B-C-D. Similarly, you can get a train TO the airport, but only FROM the aforementioned Jefferson Street Station. Last train from airport will be around midnight. There will also be two bus routes running, the 108 to the 69th Street transportation center, more or less on a weekday schedule, and a route 37 to Broad and Snyder on a weekend schedule - but the caveat again is that if you then connect to the Broad Street Subway from there you will be discharged at Broad and Walnut, and even walking to City Hall will not allow a connection the the Market Street line as there will be no service between 2nd and 30th Streets.
So far it appears that for anyone needing to simply make a connection at the airport that flight operations internally should be more or less normal. However driving to the airport that weekend will be problematic due to the closure of I-76 through Philly, coupled with the fact that many visitors will be driving to the airport as the simplest place to leave their cars and use the airport train via the papal tickets to get back and forth, meaning that if your intention is to fly out that weekend by way of leaving your car in long-term parking at the airport, you may have a significant problem.