This is awesome -- but badly needs some interface work. We've built a similar tool for our CMS also on Bespin/Skywriter/Ace. Here is a screenshot:

http://www.flickr.com/photos/gethifi/4952045778/

Little things like icons on the left are really helpful when trying to browse a file structure. In any case, I'll likely be using this once and a while in a pinch since I keep all of my client files in Dropbox.

I'm also excited for the Ace update. This appears to be using a pretty old version. Rendering text in the DOM is much faster.