Submission + - Dropbox TOS Includes Broad Copyright License (dropbox.com)
By submitting your stuff to the Services, you grant us (and those we work with to provide the Services) worldwide, non-exclusive, royalty-free, sublicenseable rights to use, copy, distribute, prepare derivative works (such as translations or format conversions) of, perform, or publicly display that stuff to the extent we think it necessary for the Service.
I think Dropbox is a great service, but what is the significance of granting them such broad usage rights?