What is the possibility of using a Python app, deployed online, that has access to a users local disk?
You could create a signed java applet that will run along side the javascript and allow access to local files. You may be able to find an applet already developed that you can call from javascript. You have to be careful with this though because once the user trusts the applet it's installed and any site can call the applet unless the applet code is restricted to a specific site.
I currently have a local python application that scans a users drive, maps it into a tree and displays this information with javascript. I would really like to try to develop something with a Drop-Box like system to manage drive trees. 
I have searched and read that App Engine specifically doesn't allow access to a user's local disk. Is there a way to use webpy or something else to access a user's local drive to create a tree directory out of it?