Cases actually wick some moisture out of the air, which helps... and when instruments are in their cases, sudden changes in temperature and humidity won't be as harsh on your guitars... so it is technically best to keep them in their cases... but it's WAY more fun to display them for a ton of reasons.
I have mine hanging as well, as seen here:
Just be careful... having your instruments exposed like this will dry them out, if you live in a cold climate and your heaters run all winter. In the summer, humidity in my basement music room maintains at about 45-50%, however, in the winter it will get as low as 20-30% and stay there unless I keep a humidifier in the room.
So, if you decide to do this, at the very least I would buy a decent hygrometer and keep it in that room so you can monitor your humidity levels... if they get too low, consider getting one of those little filterless humidifiers. They work great if the room isn't too large.