Priceline has long warned that Google's and Bing's "inroads into online travel" loom as potential threats and now it has added Kayak.com hotel bookings as a concern, too.
In a financial filing May 6, Priceline states:

Some meta-search sites, such as Kayak.com, which recently began offering its users the ability to purchase tickets directly on its website, may evolve into more traditional online travel sites with ticket-booking capability.
Actually, the reference to flight tickets was a mistake and Priceline meant to cite the fact that Kayak began taking direct hotel bookings on Kayak.com, says Brian Ek, Priceline spokesman. For flights, Kayak.com refers users to airline and online travel agency websites for bookings.
But, Kayak introduced hotel bookings on Kayak.com several months ago through a private label deal with Travelocity. Previously, Kayak had only facilitated hotel bookings by referring users to third-party websites, a process that it still undertakes, but not exclusively.
Priceline also expressed competitive concerns about Google's acquisition of ITA Software, Google's investment in HomeAway and Google's "meta-search" site displaying hotel rates and text advertisements as developments to watch.
Of course, all of this has not stopped Priceline from marketing its wares on Kayak.com, where Priceline is currently advertising its Name Your Own Price service within search results like this:
Asked about Priceline's Name Your Own Price ads on Kayak.com, Brian Hoyt, an Orbitz Worldwide spokesman, said: "We are confident that the arbitration proceeding initiated by Orbitz [with Kayak] will address Kayak's continuous disregard of its contractual obligations to Orbitz."
Orbitz claims it has certain online travel agency exclusivity rights in Kayak search results and is pursuing arbitration with Kayak over the matter.
Kayak declined to comment on Hoyt's statement.