At a university I worked at, every IP over DHCP was a public IP address. This means that all of the printers where by default open to the world. I always thought that this was crazy. Every so often a random page would be printed...
The setup was similar at my college. I'm not sure if the printers were open to the whole world, but I do know that with a little savvy (and I mean a little) you could use any printer on the campus network. While other students were flooding the library 10 minutes before class to print their assignment, I would print them out from my dorm room to an empty office on the same floor as the classroom, and just swing by to pick it up on my way to class.
I was also very tempted to just spam a bunch of gibberish to the printer on the network labeled "Presidents Office", but decided that might raise a few red flags.
Just because the addresses are publicly routable doesn't necessarily mean they're accessible to the public. I used to work at a place with a Class B block, but nevertheless advertised no routes for most of those IPs. Internally any traffic to the internet had to go through proxies.
