Host a Linux Repo and Torrents for some of the not-quite-popular distros you like.
Host a game server and play with friends, make new friends and lose false ones.
Host a Jabber/XMPP server and help freeing the Internet.
Don't use that stuff all for yourself, do good in the world. Learn something. Share joy.
I believe there's already a project like that called Movim. It's basically a decentralized social network built on top of the XMPP protocol and 100% open source. It just hasn't managed to achieve popularity yet.
As mentioned, there's also Diaspora, though that hasn't achieved popularity either.