Seriously. On a 22" monitor, it only covers maybe a quarter of the screen. I need some ammo to axe down this rule.
I'm not saying that there shouldn't be a limit; I'm just saying, 80 characters is very small.
I think the practice of keeping code to 80 (or 79) columns was originally created to support people editing code on 80-column dumb terminals or on 80-column printouts. Those requirement have mostly gone away now, but there are still valid reasons to keep the 80 column rule:
I think the last point is the most important. Though displays have grown in size and resolution in the last few years, eyes haven't.