It depends on where in PA you're driving from--it's a big state! We drove from PA (south central area) once for our honeymoon in 2003. From our house, I-95 makes the most sense, but depending on where in PA you're traveling from, I-81 would probably be better. We figure roughly 2 hours from our house to the other side of DC, 3 hours each through VA, NC, and SC, 1.5 hours through GA, and 2.5 hours into Orlando--15 hours total. We stopped in Savannah, GA on the way down, which took us 12ish hours. Savannah is a very pretty town, but if you plan to see any of the historic area while you're resting from the drive, take a tour. It's a rather difficult city to navigate because it has many squares and fountains. Charleston, SC is also a nice place to stop, but I believe it runs a bit more expensive than Savannah and it's a huge detour off the interstate. On the way home, we stopped in Hilton Head, which we think was probably a nice place, but we only saw it in the dark! We were traveling in January and we hit WAY more traffic around Jacksonville (apparently this is a very popular place) than we anticipated and it was dark by the time we reached Hilton Head. We left in the dark the next morning because we were anxious to get home and we had to be prepared to go back to work the following day. A stop in Hilton Head could possibly be done on rented DVC points, so it would be a way of starting or continuing the Disney magic!
One important thing to consider when driving from PA is traffic. Driving down I-95, you are subject to the peak traffic in half a dozen major cities. We were just discussing yesterday the possibility of driving to WDW next fall. We figured that from our house, our best bet would be to leave around 1am to drive straight through because that would keep us out of the major rush hour traps and put us at our resort right around check-in time.
