Joining the midpoints of the sides of a quadrilateral

Take any quadrilateral, ABCD, and join the midpoints of the sides to form another quadrilateral.
  1. What do you notice about the green quadrilateral in this applet?
  2. Does it have any properties you recognize?
  3. Can you verify these properties by measurement or some other means?
  4. What if you move the vertices?
  5. Do the properties you have found still hold?