No catches,,some holiday blackouts..but just the usual..I use Southwest all the time. If you get thee early, you get in line for your seat, and pick it as you are lined up. We have always lucked out and gotten good seats. When they first announced the sale (last week it was $49, and I thought that was good), there were lots of empty spaces..they are pretty full for anything this summer, but lots of great times left for Fall. They have some that are straight through (I try for those..I leave in the morning, and in 3 hours I'm there, and leave in the evening..so I get full days), and some that have connections, just like other airlines.
Right now, you get a free ticket for each 4 round trip tickets you buy, so it's a real deal!! That will soon be changing to free ticket after 8 flights.