On the flip side, it is styled very much to mimic Chrome's own editor. And that makes me wonder. When or why would I use this over what is already built into Chrome?
Sounds super hard to me, but what you built looks super hard too :)
Actually the Chrome DevTools can save your changes back to disk! It's not well known, and its fairly new so I don't blame ya.
Here's how it works: (1) make changes to styles as you do (2) you can click through to the Sources pane and live-edit styles there, just like a text editor. (3) Right click and save to disk. choose where to save the file (4) Make some more changes (5) Just hit ctrl-s (or cmd-s) to immediately save back to disk in the same location.
I just made a screencast to show this in action: http://www.youtube.com/watch?v=Qy5obNItQiQ
That's totally right and it's a very cool feature, although that will only help you if you are using Chrome. One of the things I wanted was for the product to work on any browser, and without any plugins.