+1 to everybody's feedback on the article-specific actions (and user testing – yay to data!)
This is feeling a bit too top-heavy to me. When you first load the page, you're presented with three different drop-down action menus, sidebar navigation, and the article ToC – but when you scroll down, you've only got user stuff + edit on hover. Have you explored breaking these elements apart and utilizing the space lower down in the page for progressive disclosure of less important navigation elements (maybe a quick ToC-like "navigate-to-section-Foo" affordance?), or repeating important actions from the top menus (history, watch) again? Also, to echo Brion, the sidebar feels very empty and gray when you're down in the depths of the article; it would be nice if it didn't get in the way of reading and preserved all the useful links and tools no matter where you were on the page...
Finally, call me someone who's drunk the Koolaid ;) but the article text feels really, really wide. Upon inspection, it looks like you've made the sidebar a bit narrower, which in turns makes the article text flow even wider than it currently is on talk pages. This makes it hard to read/scan the short 2-line long subsections and causes the open personal bar & edit menus to obscure article content. I know it's not really part of what you're try demonstrate with this prototype, but enforcing tighter margins would give the righthand stuff a bit more room to breathe and shine :)