[joeyo]

Historically Southwest used "point-to-point" routes heavily. Basically the plane would go A->B->C->D over the course of a day. These would be fairly short hops, maybe an hour or two typically, and passengers going all the way to D would stay on the aircraft during each brief stop. I don't think they have any nonstop across the continental US; you must make one (or more) stops.

This may have changed somewhat since the AirTran merger, but I haven't flown recently.