Although they aren't offering the $19 fare anymore (still cheap, fares are as low as $39, with no sat. night stay, no roundtrip required), they have been expanding with new cities and flights.

I had the opportunity to fly them twice and actually meet the CEO of the airline on my flight. All brand new Dash-8 turboprops, 50 seaters, leather seats, in-flight snacks, flight attendant. They are HQ in Hartford, CT.

They tend to fly alternate city airports, like Wilmington, DE instead of Philly (almost as close to Philly as the Philly airport). They also fly to Trenton NJ, Albany, Buffalo, Norfolk, and Islip.

latest press release:
see: http://biz.yahoo.com/prnews/990615/ct_shuttle_1.html

Web Site:
see: http://www.shuttleamerica.com/

sorry - No Freq. Flyer program, yet (but the prices more than make up for that)