Yeah we've had this for sometime. That demo of hula (for those keeping score at home) is just a UI demo and not working against a real calendar server. You can drag events and even rubber band them to adjust the start/end times.
You can see this on our demo:
http://www.zimbra.com/demo
Remember you can only move events you created so the events on the demo that are not created by the demo user won't be draggable. You can always create some events yourself and practice dragging them.