When it comes to making choices, people often default to "safety in numbers", i.e. what everyone else is doing. While the internet is widely applauded for bringing lots of information and reviews about products, it also allows you to judge what's most popular. For example, on Flickr you can see what cameras people are using:
Amusingly, I felt somehow good that I had bought the most popular camera without even knowing it was the most popular or "best" by popular choice. (Although I'm sure if I'd bought one of the others, I'd now be telling myself I did good not buying the camera everyone else bought!)
The internet is providing us more and more interesting data whether we use it for personal decision making, product decisions, political motives, convincing others, …