I sometimes believe the airport you are flying to/from has a lot to do with the time changes........not to say the airport is making the changes on each individual airline, but, naturally the busier airports tend to have many more changes on a daily basis than a smaller regional airport. We've flown Airtran on our last two trips from ABE (Lehigh Valley International) and from the time I booked the schedule changed by only 2 minutes.......which doesn't appear to be the case for flights in/out of PHL ever. We also absolutely love to fly SWA, but, unfortunately that's also out of PHL.........and on every single return trip to PHL we experienced major delays.........didn't matter what time of year, weather conditions, etc.........so I'm convinced the airport (i.e. the number of airlines, more flights, etc.) has a major impact on the timeliness of the airlines.