I wanted to make my OSX Desktop a folder in my Dropbox, so it always syncs.

• I cleared all the files from my Desktop to ensure I don't delete anything when I do this.
• Remove the default OSX Desktop folder, which is in your /Users/<username./Desktop. So, I sudo rm -rf ~/Desktop, which is a DANGEROUS OPERATION, so you may want to read about it.
• Then, ln -s /Users/<myUserName>/Dropbox/Desktop /Users/<myUserName>/Desktop. This creates a link. This creates a symbolic link where the default desktop used to be. It now points the Dropbox folder.

Now, OSX displays the contents of the Desktop folder in my Dropbox as my standard Desktop.

Easy enough ~