I'm in the middle of a three-week work vacation to Europe. I usually use Travelocity for booking airfare and hotels, but I found that a lot of boutique hotels in Europe were on Booking.com (which is in the Priceline.com family) and not Travelocity. A few "social" features of Booking.com really caught my attention. I am not sure if they are on Priceline, its parent company, or not. But they are on Booking, and used to great effect.
I'll start by saying that over the last six to 10 years, everyone has tried to figure out how social networking could be harnessed for e-commerce. Generally, this has led to unimpressive "group shopping" functionality, or mundane "tell a friend" features. Booking.com takes an entirely different approach. Instead of trying to connect you with other people while you are shopping, the system simply lets you know what other people are doing in regards to the hotels you are viewing.
For example, take a look at this screen capture. On the top right of the screen, while I was viewing this hotel in Barcelona, a little notification popped up that the most recent booking for this hotel was made at 16:07 by someone in France.
