I have used priceline twice now in the last month thanks to being pointed in the right direction by Scotty. I used bidfortravel.com to learn the ropes.
I scored to great deals IMHO for my vactation in May. The Veneitan for $79 per night and the Marriot Mountain Shadows, Scottsdale for $79 also.
I wouldn't use priceline for flights as I always need flexability.