I'm interested to see that they do historical rate comparisons. I thought about implementing a hotel rate searcher which flagged deals that are better than historical prices, but was put off when I saw Bing held a patent related to their Rate Indicator:
http://www.bing.com/travel/about/ourTechnology.do?FORM=TRABV...Edit: it looks like Bing's patent relates to predicting future prices (when will be the best time to buy).