I just upgraded to the latest version of the module, and the visual editor still does not seem to be complete. There is nothing below the "Attach existing file" header. Looking at the plug-in code, it looks like this has not yet been implemented? :-/ All of the .filetree ul in editor_plugin.php are empty. (I am using Firefox 10.0.4 and Chrome 19)
Also, once this feature is functional, it would be mighty handy if there were a simpler widget that would only allow one to attach existing files. I would prefer it if contributors could not upload arbitrary content to my server, but attaching existing content to posts is fine. (Even better if such a widget were configurable to only allow attaching of files from a certain section of the filebase directory tree).