On WPD, the breadcrumb trail works ok to get back to where you've come from, but it is currently hard to get to anywhere in the site from anywhere. WPD could do with a nicely styled dropdown navigation menu, to make getting to different content sections a bit more immediate, e.g. I want to get to CSS property references.
I reckon this menu wants to go just above the line with the breadcrumb trail and the editor tools on it. I'll create a quick mockup to show you what I mean.
Created attachment 1262 [details]
rough mockup of site wide WPD menu
Mockup created, as promised.
Please note that as coded in attachment 1262 [details], this menu will be ineffective for users of touch interfaces. Perhaps an approach that uses click instead of hover to expand the menus? Hover gets you nothing in touch--at least with today's touch devices.
That's a good point Eliot. More work needed.