1. Don't make the demo look done,
2. How 'done' something looks should match how 'done' something is,
3. The more "done" something appears, the more narrow and incremental the feedback.
Following Michael's post about hildon theme tools, I have been playing a bit with the tools, and started to work on... a sketchy theme. Sketchy is based on Plankton. The current release has basic support for "desktop", menus, dialogs, buttons, scrollbars, and banners. More to come!
Here is a preview of the result:

I could get this in a couple of hours (I am not really an artist specialist). The tools make it really easy to make a complete theme, BIG thanks to Michael and tigert :-) I encourage anyone to give it a try! Michael promised some tutorial, and I'll write more later about my experience.
Here is the sketchy theme package (and its source). You also need the hildon theme cacher to be able to install the theme on your N800.
Enjoy!