Nice, we're evolving the same mechanisms for quick herd notification that animals have.

This is why humans and animals scream when we're in danger (not because screaming is a very effective danger mitigator), and this is why some animals jump in place when they detect danger (http://en.wikipedia.org/wiki/Stotting).

We've had these two signals exploiting our vision medium, and our sound medium. And now increasingly, we're adding signals exploiting our digital network medium.

As those become more and more commonplace they have a very tangible effect on our society. Think Twitter riots and what not.

BTW, people in Japan get an instant smartphone warning when there's an earthquake.