There's now a blue wedge in the upper-left corner of the screen in all the web apps and in the OPML Editor control panel.
When you click the wedge, the menubar is hidden. Click again to show it.
You can see this on the World Outline site, but it's visible everywhere. It's a fixture (which is more than a feature).
We needed this in the world outline, where we want to give each user full control over the presentation through the template. Having our menu at the top of the screen as a fixture wasn't going to work very well.