I have over 1100 hotel nights booked through Priceline and Hotwire over the past 9 years. I can count on one hand the times I was unhappy with the hotel I got. Like they said above, do your homework on www.betterbidding.com and learn how to use free rebids to bid the bare minimum.

Priceline can also get cheap cars as seen on BB.

I only once bid for and got a flight. Ended up with Air Canada from San Francisco via toronto to Rome, at very convenient hours. Somehow I even got full mileage credit for the trip. Saved about $300 off the lowest published fare. Flight bids since then were rejected up to the point where it no longer made sense to bid higher, and then I stopped even trying.