I do the same thing. I set a vertical guideline to 120 characters. Depending on the codebase I'll turn on wordwrap at 120 characters too.
I like a 80 column soft limit which I usually stick to and a 120 column hard limit which I use when I feel splitting the line and indenting would harm readability.
This so much. Rather than "don't exceed 80 characters" the guidelines say "break up complex statements into multiple lines if it contains complex logic" and say that the target should be 80 - 120 chars per line.
Just for comparison, I'm reading your comment at 140 characters width and I don't have much problem with that. I like my web text to occupy most of my screen. Only if I stretch it across multiple monitors to 160+ chars per line does reading become a chore.
But it is a personal taste.
Personally, I prefer the 120 characters per line guideline. Most code I see starts looking very ridiculous when trying to accommodate the 80 characters max width, and it starts becoming hard to follow lines when exceeding 120 characters. So, to me a soft 120 characters guideline is the nice medium between the fact that it's no longer 1980 and the need to make lines easy to read.
Also, in most cases readability has almost nothing to do with line width (in fact it can suffer greatly from too much line breakage), and everything to do with how the programmer chooses to structure their code, aided by language idioms.