I used code from various applets as I couldn't find great doco on the web. I ended up finding some decent stuff from the GNOME3 site though, at least for the GSettings stuff.
I looked through the code in the following applets to help me learn what to do, and in some cases may have used some small segments of code from these applets:
The weather applet was clear that it's licence was GPL3, so the licence for this applet will fall under GPL3 too (incase I used some code from there, not sure anymore).
I also retrieved the really nice looking icon from: http://findicons.com/icon/94179/previewer?width=16 Icon Author: http://schollidesign.deviantart.com/
The icon is also GPL licenced. I wanted to use it, but after 15 minutes of trying to figure out how to display a bundled icon with the applet, I gave up.
Please drop me a note if you know a nice way of doing that!
You can reach me on e-mail at (remove the whitespace and convert the AT etc): mick saunders+path-mon AT gmail dot com
I assume there is a simple way to do this. I hope you will excuse my reluctance to learn Java.
Making a copy of the applet should work fine until you restart cinnamon. On restart the second copy (path-monitor2) might not load the entered path. If this happens you probably need to modify the gschema to handle another "watchedpath" and recompile it, and then point the path-monitor2 at this other 'watchedpath' key. If you really want to get multiple instances to work I can post some more detailed instructions.