bw100 - 9:34 pm on Jul 28, 2011 (gmt 0)
I just did a quick check for New York City and Las Vegas. Very sparse listings right now, and the "Book" button is not active on most of the hotels displayed.
When the "Book" button is active and clicked, the displayed box is labeled "Ads", and contains links to a selection of hotel booking sites such as Booking.com, Hotel.com, Hotel club.com, and Expedia.com, as well as the hotel website. It varies with the hotel. Selecting one of those options takes you to the page for that hotel at the selected booking site. I checked about a dozen different hotels, and did not experience an option of booking directly.
At first glance, they seem to be using this to sell ads right now.
But, I wouldn't rule out some affiliate relationship with the booking sites.
And, of course, handling the booking could be in the cards ... later.