I use a soft-ish guideline of 100 columns per line, but I mostly code in C# at work, so normally namespace/class/try-catch is already 3 indentations, and 80 chars is simply not enough for everything.
I do my best to keep it between 80 and 100 chars. With a horizontal screen resolution of 1920 pixels, 2 pages of such code fit nicely side by side.
The other problem is that 100+ column lines are just flat out hard to read. It's hard to follow text that far across these screen. A few years ago when I was working with Objective-C I came across methods used with each variable on one line and really grew to like that.
It's similar to the way source code is laid out in books. But is that because the code is more readable that way, or is it a consequence of the layout? Books are taller than they are wide and usually have generous margins.