I have found that the "power users" are moving towards multiple monitors and fill a single screen with a browser.
I'm also always doing several things at once, so I'll tend to fill up one browser window with tabs related to one topic, then launch off on another tangent and fill more browser windows with more tabs. And that's just on one of my 9 virtual desktops. So having only one browser window visible makes it hard to keep track of what window has what information.
My usage pattern is not typical.
Nonetheless, I think that's a small price to pay for being able to fit a vertical PDF on a monitor nicely.