wait, really? If you have the desktop client installed, you can just download it to dropbox like it's any other directory on your system. It's fantastic. In fact, I never use the DB web client.
Of course, that's been the #1 use case for Dropbox since they launched.
The point is that they are looking to create 'dropboxes' across the open web, so that you don't have to actually download stuff at your end first. So you could have a folder which you chose to NOT sync with your computer, but instead only used as a web-stuff repo in the cloud, for example. That use case doesn't exist today.
