In 30 seconds your picture is now on the computer of thousands of people...
I dropped out of college (computer science) in 1995 to start an Internet business. Bob Metcalfe informed Infoworld readers about my progress. One thing Bob is famous for (besides Ethernet) is popularizing the "Network Effect" when it comes to Internet. Basically as you increase participation the Internet becomes more valuable/useful. I could setup a forum for a few friends, but it would not be as useful/valuable as using apug/flickr/lff. You can share stuff with friends, and make other valuable friends in the bigger forums. Sort of like using the public phone network is more useful than giving my best friends walkie-talkie radios for when we wish to talk.
I don't have hot vixens posting mirror shots on my facebook; maybe I should go back to college.
You can also make private equivalents of facebook using Yammer; such as for the people in your workplace. It's horrid. Everything bad about facebook fully privatized. Forums and other web software can be useful ; just gotta think about your plan before you act because the software's just a tool.