I was looking through the settings in Firefox earlier today and ended up clicking through to one of the help pages (Firefox's performance settings) which, IMHO, has a bit of excessive whitespace usage going on. After the fuss that browser vendors made about reducing the amount of vertical screen real-estate used by their browser chrome, it seems a bit rude to be using quite so much for the branding/top-hat in content pages. Here's a side by side comparison:
That's quite a bit of extra content (16.7% to be precise-ish) displayed, just by not having the browser brand take up an entire strip of the page, on my 1920x1080 screen. It's a little bit like the recent Skype client that was more white space than conversation, just not quite as bad.