Terms of Service are the same for WebDAV as for anything else: the storage we provide you with is for the express purpose of running your website(s) hosted with us. If what you're after is personal file storage, we provide some of that through your Backups User. If that doesn't cut it, there are some other excellent services online which provide that sort of service, such as Dropbox.
Once we have Ceph fully operational, though, this situation may change. Stay tuned.