Would it work to take the train one-way and fly back? (or vice-versa). With SWA flying PHL-PIT, getting a good one-way fare shouldn't be a problem.

The PHL-PIT route is one of the most scenic east-coast routes. Starting from PHL, you head west through the rolling Lancaster County farmland, then cross the Susquehanna River on the famous Rockville Bridge. After that you follow the Juniata River for a long time, through the Allegheny Mountains, round the spectacular Horseshoe Curve and on into Pittsburgh. I love this route.

On the other hand, it's not exactly high speed rail. It's a pleasant change from air travel, but you might get a little antsy when you're sitting on some siding near Altoona waiting for a freight to pass.

And of course, you also have to consider the fact that there is one train a day, versus probably 15-18 non-stop flights each way. (US Airways and Southwest) So convenience-wise, the plane is definitely tops. But if you have the time, you should definitely give the train a go in at least one direction.