UPDATE:
QJ
Here's a quick off-screen gameplay video for Kingdom Hearts: Birth By Sleep. It's so short that it's over before you can even say "Keyblade".
In it, we see Ven battling some Heartless... or at least, I think they're Heartless. Much to say I don't recognize these types of Heartless from the previous games. Also, it looks like Ven's quite a ways up his skill tree already.
Square Enix probably gave the demo some snazzy moves and advanced skills (remember how Sora had to unlock/learn those dash abilities in the previous games? - in this demo, Ven has them already) so that people trying out the demo know how combat feels like with all the cool moves.
Oh. And one last thing... The PSP unit you see before you is a 3000. Heh. Envy...