On question pages, prioritize the right column over the left.
In the animated images, the right column always drops out first, and then eventually (as the window narrows) the left column is replaced by a toggle control. When looking at an individual question, though, the important stuff that isn't Q&A itself is on the right -- age, last active, and especially linked and related questions.
When I'm looking at a question I care about that stuff, not about other tags/users/etc over on the left. Please don't sacrifice the useful right-column information to the stuff we don't care about right at that moment from the left column.
And please don't do this by keeping both around and making the actual Q&A part unmanagably narrow. This is a case where the left column should be the first thing to get out of the way.
A broader change that I'd like, that would also accomplish this, would be to always make the left column collapsible, like in the narrow case in the animated images. If I can always collapse it -- because 95% of the time I'm not going to use it anyway -- then I automatically get the desired behavior on question pages.