I've set my entire Dropbox to upload files as "online only". Yet, Dropbox still appears to be keeping all of the files on my hard drive and I am out of space. When I open up Dropbox, I can see everything has the cloud icon, so I don't understand where to delete the files. Please help! I am unable to do anything until this is solved.
There's a hidden .dropbox.cache folder in the root of your Dropbox folder. Files in this folder get purged about every three days. You could check the size of this folder to see if it's the cause of your low disk space.