As both Sean and Gio have said, the quick register does take up a lot of room.
While collapsing it sounds like a good idea, I think this will probably remove it's effectiveness, so the best strategy would be to restructure it a bit to get rid of wasted space.
eg, you could have:
username - password - confirm password - image
email - confirm email - agree to rules - submit.
This gets rid of a whole row there and so moves everything else up a bit.
Your footer does need some attention.
Other than that, a very clean style, well thought out.