Personally I don't use Priceline for air travel because I want to have greater control over scheduling, stopovers, etc.,, but it's great for hotels and particularly rental cars.
Two sites any Priceliner should bookmark:
http://www.biddingfortravel.com/
http://www.betterbidding.com/
They help you beat the system since other people tell you what they've been bidding and getting, plus you get a list of potential hotels in each place and their * levels.
Anyway, slightly off topic post, but good info for someone who's new to PL.