I've been using it for a while now. The new position of the new tab button on the top left take some getting used to but I do think it looks really great.
I find useful from time to time (when i am using the mouse to browse anyways). that's in part why i never really got comfortable with the "tabs in titlebar" thing, as i am used to being able to double click the tab bar to get a new tab. But applying that to the tabbed titlebar instead toggle the maximized state of the window.