title: UIView's frame, bounds, center, origin, when to use what?
body: <p><code>UIView</code> has the properties <code>frame</code>, <code>bounds</code>, <code>center</code>, and <code>origin</code>, and they all seem to be interrelated.  Most of the time, I deal with <code>frame</code> when setting the position and size of a <code>UIView</code>.  I understand that <code>frame</code> is using global coordinate system and <code>bounds</code> is using coordinate of the local view (therefore its x and y are 0, but not always), but it's still confusing to me when to use what.</p>
  
  <p>Under what context (and what's the right time) the other properties (<code>bounds</code>, <code>center</code>, <code>origin</code>) should be used?</p>