The Enable User Data setting allows you to pass arbitrary data into the user-data key of the DigitalOcean Metadata service. It is available in regions that are running v1.5 of our backend.
You may run this command on a droplet, to retrieve the user-data that you supplied at its creation time:
curl -w "\n" http://169.254.169.254/metadata/v1/user-data
Currently, the Enable User Data setting is only required for the clustering of CoreOS droplets. For more information about using the setting with CoreOS, read this tutorial: How To Set Up a CoreOS Cluster on DigitalOcean
Eventually this will be available on other OSs as well. Check out the Cloud-Init docs for more information.