I see Kayak.com have rolled out with a ppc bid engine for their new site:

Travel-search player Kayak.com is expected to launch a beta of its self-service auction-based bidding environment for hotel and airline advertisers today. The debut of the CPC ad tool comes in conjunction with the official consumer launch of the site itself.

Hotel chains and individual hoteliers can bid to appear higher in results when Kayak users search for accommodations options. Paid results are displayed with a "K" symbol to inform users the hotel displayed is an advertiser. Hotel marketers can tailor bids so their results appear higher for certain stays, lengths of stays, particular markets, or specific hotel brands

So what's the deal with them, does anyone have a little more info on Kayak?