Synchronize a folder outside the default Dropbox's directory

[CONTEXT]
You want to synchronize a folder with Dropbox, without move that folder to
the default  Dropbox's directory
[HOW]
Create a symbolic link from the folder that you want to synchronize to the Dropbox directory, for example

$ ln -s /path/to/folder/to/sync ~/Dropbox

The permissions of the files or folders should be (at least) owner:r/w, group r/w, and others: r
-rw-rw-r-- 

[SOURCE]
http://www.dropboxwiki.com/tips-and-tricks/sync-other-folders