Dormlink is a social network that I made with with Bryant Tan. It's devoted to college students in dorms, currently in operation at Stanford for 5 freshman dorms and 180 freshmen. The Stanford Daily wrote about it here.
We made the front page!
I designed the site, built a php framework, and constructed the database. It's now being hosted on a server in my dorm room. You can try it out using the demo link at the bottom of http://dormlink.me/.
UPDATE (Mar 7, 2012): We took Dormlink down last summer when we went home, and we haven't put it back up since. A social network for your house would clearly be too much... one for your dorm further stretches the usefulness of the Internet.