Item's that are popular on a social networking site depend on what people are looking for. It's really up to each person's own interests. Some items appeal to a larger audience of people. But usually they are only temporary until the next big thing. This changes daily.
There are also many unusual items that some of the more open-minded people come up with. One such item is musical underwear. No, I could not stop laughing either. I would write more about them, except I can't make it past the title.
Some items have photos that help explain certain steps to the reader. A few have been edited with words, arrows, and boxes to make specific points stick out. These photos can be very helpful and interesting.
Members can share and request information in a variety of ways, depending on the kind of website. In my experience there are three types of social networking sites. The first are sites like Myspace and Facebook. Which mostly focus on social communication, through status', private messages, photos, and instant messages. The second type is a site like Instructables. Which allows you to make an article with photos and links. Then users can comment on these articles, and the creator can comment back. The third kind is a forum. An example of this is Monsterfishkeepers.com. A forum is similar to a site like Instructables, but is focused more on learning through constant conversation instead of articles. It is also much easier to request information by making a question post.
Social communication sites are probably the most popular form of social networking, but the other websites are all great tools for locating information and finding people to talk about your hobbies with. In short, social networking is a great way to gather information and keep in touch with friends, or make new ones.