I was able to get the Westin LAX this Tuesday night for $79 thru Travekocity vs. $139 via AMEX (I veen had them call the hotel directly and see if they could get that rate for me and the answer was "no" -- the reservation agent couldn't even see that rate).
I then got the Sheraton City Center in Salt Lake on Wednesday for $95 vs. $119.
You are right, that you lose if you need to change/canel...but unlike Priceline, you can pick your hotel, and I believe you get Starwood Q points, which you don't with many of the discount hotel sites.