Mac: Sync to Dropbox

From http://www.macosxhints.com/article.php?story=20090929052128498

This method means no need to have the file copied - it uses symbolic links.

To do this, you need to use the Terminal. Since Dropbox allows you to choose where your Dropbox folder resides, there's no "one size fits all" solution, but here's the general syntax (replace username, foldername, and path/to/dropbox with your own values):

ln -s /Users/username/Documents/foldername /Users/path/to/dropbox/Files/

You can also drag the source and destination folders into the Terminal window instead of typing the paths. Note that foldername has no trailing slash (/), but that Files/ bit does -- this is very important!