Unfortunately, at my current job, we don't seem to believe much in unit testing. There's some indication this may change in the near future.
Additionally, I have two screens, and since I mainly use a tiling window manager, 80 columns works... okay. But 80 columns isn't usually where my splits end.
Interesting point with the same file in columns. It's rather that I do that. More often I'll be looking at the same file across two branches. I am kind of surprised that we don't see more plugins doing 80 column lines, in sequence, to fill the screen however. More lines on the screen seems to be the craving that vertical monitors + high-res monitors aim to satiate.
80 columns of text is wonderful in my dual window vim with NERDTree on the left. All my screens are some version of the 1680x1050 aspect ratio and it fits perfectly. I'm always using 2 windows for simultaneous code/test writing, diffing, and multiple windows into different parts of the same buffer, multiple files open etc.
And you know you can put different parts of the same file in columns too? I often need to write code that is coupled to another part of the same file.