Well, actually, I believe that even worse would be that your offer was accepted and you were given a routing that had a 20-hour layover or any number of other horror stories! I use Priceline all the time for hotels, and occasionally for rental cars, but never for air. I'm sure it can be great if it works, but.......
I had a friend that got a great deal on tickets on priceline by knowing what the airline schedules were and narrowed his acceptable time window to allow only certain flights. It worked for him on overseas flight that time. I also talked to a coworker who got the "horrible routing/long layover" and didn't save much money.
Personally, I've never tried Priceline with airlines.