Design Patent Application

Has anyone already filed a design patenta

Yes, and it's a pain in the _ _ _ to do. The thing to remember that for the element to be actually accepted and granted patents, you must describe in detail how absolute it is supposed to work, and your diagrams should be detailed and well, showing all stages of operation. This is what makes your invention different from the potential of a patent could be filed for the same thing by someone else. Do not copy or form as something you've seen and improve the patent will not be granted because it is called infringe on the patents of other items.
Apart from this, complete all forms and as I said make good diagrams, and then when you send it to the patent office so that you send all documents certified, insured, return receipt requested, and mail recommended. This way you make more explicit in a way that you sent the documents to a certain date and was received by the Patent Office.
Good Luck

Yes I have. I'm still waiting for the U.S. government to tell me if it's legal or not.
Patent Pending ... are the magic words