Not looking where you're going is dumb, but I think the city leaving a manhole cover open, unattended and not blocked off is even dumber. This isn't like that idiot that burned herself on hot coffee - I think a lawsuit for this kind of carelessness on the city's part is warranted. I think the txt-haters would be okay with this lawsuit if, say, a blind person had fallen in. I think it's reasonable to expect that you won't fall into a manhole if you're not looking at where you're going. Maybe you'll walk into a sign post, or get run over by a car, but falling into a manhole is totally the city's problem.