This is what Rotten Tomatoes’s homepage looks like, maximised, in its own window, on my computer.
This is what it looks like with the chrome (the browser’s toolbars and UI widgets that can’t be helped) coloured in blue, and areas plastered with advertising that I don’t give a shit about coloured in red.
That’s a lot of wasted screen space.
(Also, it knows who I am through Facebook’s creepy omnipresent-login facility. I hate that. Whenever I see one of those I’m irrationally terrified that it’s going to broadcast every page I view to all my Facebook friends indiscriminately and indiscreetly.)
Update: Yes, I know that if I were to install AdBlock, all that wasted space would magically go away. Considering, however, that 90% of Firefox users don’t have AdBlock installed, that’s still a lot of pissed-off users.