Sometimes even a few months out, holds mysteriously get canceled after only 24 hours. I would never rely on USAirways' 72 hour hold for anything other than simple itineraries that you could re-create easily. If you've managed to price out something crazy that you're pretty sure you'll fly, ticket it on the spot. Unless you want to spend another stressful 1hr+ on the phone with them. Actually more when you factor in having to play agent roulette.