I use a vertical display for my browser (so 1080 px wide), see screenshot for the aspect of SO in my browser.
While wide margins are probably fine on wide displays, here the amount of margins on both sides really reduces (and vertically squeezes) any content, to the point that only about 30% of the screen is used - that feels like a waste. I'll definitely disable the left navigation, but if you want the website to be responsive, I'd recommend to start removing margins at wider displays than now.
feature-request user cards next to each other.
I think there is somewhat of a misconception around responsiveness. Just making things more vertical doesn't make necessarily make them better on a less wide screen. What you want is wider content, better use of space.
On the same screenshot, you can see that the editor usercard is now vertically stacked with the author usercard. This wastes even more space, even though there is more than enough space to fit them horizontally. And again, this is a copious waste of space.
