I ran two quick tests on ORD-SFO. One for 10/13 to 10/16, one for 8/30 to 9/1. I couldn't put in tommorrow as a departure date. Both were all-jet, no red-eyes, 0-1 connections.

I got a price of $219 for the 10/13 trip, and $239(!) for the 8/30 trip. Best prices through traditional means for 0/1-stop were $321 and $673 respectively.

I would not use hotwire (or priceline for that matter) for leisure airfare - I have to give up too much control of the situation and too many perks to justify saving $100. But I do see a niche for short-notice travel where hotwire would be a useful place to check along with priceline.

If nothing else, competition in the discount space is good for everybody.