I use screen very heavily. One of my favourite although somewhat frivolous uses is running irssi on screen from my home box. I have irssi configured to set my status to away when the screen is detached and having the chat session be persistent is a huge help.

Also I've used screen as a poor mans daemon tools to run various apps in the background as a service. I even at one point had a skeleton init script that used screen to run any command as a daemon. I should see if I can find that actually and get it on github so I can find it the next time I need it.