IF NOA was smart this is what I think they should do (in the US/PAL regions anyways)
November(around Thanksgiving)
Release D/P
December (early)
Release Pokemon Ranger
Make the Manafi quest available as soon as you beat the game.
Nintendo advertises that by connecting pokemon ranger and D/P you get the ultra-rare pokemon, Manafi!!!
Then BR around January/Feburary
why not have a bonus disk that has the item to catch Darkrai shemi(sp?), or Aruseus
Or advertise it with a different rare pokemon with a special move and an item. (My hope would be a leichi berry).
Then for those who don't pre-order they could put one or two of the following in the game. Deoxys, Jirachi, mew, or celebi.