I have often used hotels.com but it became increasingly obvious that they almost never have the lowest price. I came to using the site just to find hotel options and then book them elsewhere but recently I gave them another try. I was going to San Francisco and booked at a mid-range hotel for 2 nights. You cannot cancel but I did know that they had a price guarantee so I didn't worry. Within 5 minutes another site showed me the same room for a total of $30 cheaper. I went to hotels.com and filled out the price guarantee form which included the site where the cheaper price was found. Later that day I received an email saying that they would not honor the price guarantee stating that they "could not locate the rate." They sure didn't try very hard because I signed right back in and found it. No special rate, just the posted rate from before and it was still there.
Don't use Hotels.com!