Things like major storyline info, like what heppens to Master Xehenort, Venitus, Ven, Aqua, and Terra. Certain situations that involve Disney characters won't be as bad, but you get the point.
Plus I can imagine them being there. It should be amazing when we see it. And I really hate Venitus just being a jerk. Not because he's evil, but because he won't show people his face! Well you know what? I'm not going to see his face until I play the game. NO ACCEPTIONS.
You mean how they'll meet Ventus and what world they live in? I'd be suprised if they lived in Twilight Town... actually, that's a big possibility, with Axel knowing about that spot on the tower in 358/2 Days.
Yeah... Apparently Axel's and Saix's somebodies will appear in BbS, being around Ventus' age. They'll have the same hair, though shorter, but won't have any markings or scars on their faces.
My brother's girlfiend has the same birthday. By the way, she used to live down the street from Taylor Lautner. It's true! I even went to the same Christmas concerts as him!