If you find your Dropbox is stuck at 100% CPU and constantly ‘Downloading file list’ on your Mac, and you’ve tried all of the unlink/re-link suggestions, be sure to check you don’t have a symbolic link in your Dropbox folders.
I did (from a downloaded website backup), and my Dropbox was stuck synching for weeks.
Run the following from Terminal to search for symbolic links, then delete them (or zip up the folder in my case, then delete the files).
find . -type l