Priceline is a bit of a gamble for airline tickets. You can usually find rates about 30% lower than standard (check on betterbidding.com or biddingfortravel.com to see what others in your area are getting), but you're completely at their mercy with regards to flight times. I've used Priceline once for a flight, got decent flight times (6pm outbound, and 2pm inbound), but I wasn't in a hurry to get anywhere, otherwise I could have gotten much better flight times by not using priceline.