One of the new functions of this area is that it is tied with your gallery uploads.
EXAMPLE: If you JOIN the challenge and UPLOAD your CHALLENGE ENTRY to the gallery, there will be checkboxes during the upload process for each challenge you are registered for.
Select the appropriate challenge for your upload and SUBMIT your image. Your entry will auto populate here: http://www.scrapbook.com/gallery/challenge.html
(and in a larger version in the "view details" area of the challenge).
It's a really easy way to see what registered participants have uploaded for the challenge.