I often browse JSE on my smartphone (Lumia 920), and although the mobile version works fine, some of the posts are impossible to read due to long URLs and code blocks expanding the viewport beyond the screen. Here's a screenshot from a random answer that causes this problem:
Parts of the text is cut of, and without scroll bars it just can't be read. Zooming is not possible either.
I don't know if this problem is specific to Windows Phone (unable to test on Android/IOS at the moment), but it makes it a tiny bit harder to browse the site on a small screen.