Looks really good. I had high hopes for Bespin, but I haven't heard anything about that in some time, so I suppose I'll start watching this project instead.
I know it's based heavily on GDocs, but my workflow is based around Dropbox. Maybe something could be rigged up there.
Bespin merged with "Ace" - the new project is at http://ace.ajax.org/ or https://github.com/ajaxorg/ace.
As an aside, I was sad to see Bespin go. It used canvas for rendering, while Ace uses the DOM. While the Ace team had good reasons for this, Bespin just looked so.. pretty..