Event or category specific Custom Fields. If I order them in one way for one event, I might not want to order them the same way in another event. Not just order, but I do most of my registration in custom fields and lots of them need to be different from each other. I put in specific text fields to break it up and give instruction as they go through. It would be nice to be able to organize them.
That would certainly be a great feature. Instead of just an "Additional Information" section, the registration page could include multiple sections based on category. There should also be an option to go to the "[Next]" page for the next category. I've seen some registration services that based their process on this model and it's very user-friendly and logical.