The BBC now have a report at
BBC NEWS | Americas | Hole in US plane forces landing with a picture of someone looking at the aircraft from the outside that shows nicely where it is (just in front of the vertical stabiliser).
They missed the obvious headline though: "Hole appears in aeroplane; investigators are looking into it".
ETA: it seems to be remarkably square. I bet it ruptured and then tore along the approved lines as Boeing intended with their design.