The official line from Pokemon about the delayed release of Pokemon bank is this:
"As you may know, we are currently experiencing a large volume of traffic on the Nintendo Network service. Due to the high traffic, we are postponing the launch of Pokemon Bank and Poke Transporter until further notice,"
But the truth is: THERE IS A SERIOUS FLAW WITH THE SOFTWARE THAT WAS PICKED UP BY JAPANESE USER TESTERS.
Apparently there was a leak that the flaw was so serious that release has been postponed not days... But MONTHS!!
Pokémon Bank was designed to serve as a useful tool for Pokemon players who like to catch many varieties of Pokémon, or if you are raising an army of Pokémon for epic battles and comps that lie ahead!