A friend of mine was recently looking for a SFO-SLC flight outbound 12/23, return 1/1. Best prices (inc. taxes, fees) were:

DL, UA (via their web sites): $188
Hotwire: $140 (times, airline unknown)
Priceline: $105 (UA nonstop flights at reasonable times)

Since I know the Priceline price, obviously my friend tried Priceline and got it. She's a very price-sensitive student so was rather happy with the results. I was surprised that the discount was so deep on peak holiday travel days. Anyone know if UA gives miles on Priceline tix?