The social part is, imagine like a github, where people put up code and you can see it? Same thing with stackfu. People can put up stacks and you can deploy them to your server.

Example: A user made a stack for Rails, you need rails, you go and deploy the guy's Rails stack. You'll be able to make a copy of it, edit it, review it, and make it yours if you want, fix it update and push your own version so other people can deploy it.