While developing a project over the past year I've been abiding by a Netbeans IDE coding style. This style indicates lines of code should not exceed 81 characters in length. The ominous red line down the screen indicates when you have broken this barrier.
My question, is this still relevant with modern monitors?
I think its relevant to readability. If its just a long string like an error message or something I wouldn't worry about it.
But if you are cramming a bunch of variables and function calls, or function call paramaters, on to a single line, then I would call that a readability problem.
New lines are free. Time reading and understanding another's code is not.