Members of the site each have a user profile and can upload research output including papers, data, chapters, negative results, patents, research proposals, methods, presentations, and software source code. Users may also follow the activities of other users and engage in discussions with them.
Here is the official word from Microsoft TechNet, The C:\Users folder is shared when any sub folders from C:\Users\<username>\ is shared. The article is stale and mostly unhelpful, but worth knowing to complete the story.
Creating a Shared Folder. Setting up a shared folder in Dropbox is easy. Add the files you want to share to a folder in Dropbox on your computer, then right-click in the folder, select Dropbox, and then choose Share This Folder.