I’m putting the final touches on the codex theme today, which should be live at some point this afternoon. Once that is activated the docs tab will be consistent with the others.
The demo tab should be a simple one to solve – I just need to add the site header to the home theme.
Looks great. However, for the Demo page, I would add a page with an overview of the demo (instead of linking to it). Say something about what version it is (or if it is updated on nightly builds, whatever) and give a few points of what to check out. When I registered, I had an idea of what I wanted to look at, but it would be cool to see what you want us to look at. Make it a show off page.