Dropbox has teamed up with Facebook so that you can do cool things like add files from Dropbox to your Facebook groups or send shared folder invitations to your Facebook friends. The first time through, you'll be asked to allow Dropbox to access some information about your Facebook account.
With your permission, Dropbox will be able to access the following information about your Facebook account:
Facebook does not have access to the contents of your Dropbox. When you add a file to a group, Facebook receives only the link to the file, some basic info about the file (such as name and size), and the ability to display a small preview. The file is hosted by Dropbox, and Facebook does not receive any other information about your Dropbox account.
When you add a file to a group, members can see your post with the link to the file, but they do not have access to the rest of your Dropbox. Please note, though, that they're free to copy the link and post it elsewhere. You can learn about how groups work in general on Facebook's website.