The official opening day is
June 15th. Make sure you don't plan to go to DCA on June 14th as it will be closed to the public "To accommodate a media preview and make final preparations"
I just saw a very nice preview here:
http://www.youtube.com/watch?v=nG6bnsty02s
Looks like things are coming to life just as they designed them. I look forward to seeing these new areas and attractions!