A while back, on this very site, a sort of debate flourished about Twitter. Does it matter? Is it useful? I like it. I don't. It's crap. It's great.
And so the discussion continues.
However, a journalism student from UC Berkeley found Twitter to be of real use when he was swept up by Egyptian police while filming a protest. By tapping out one single word on his phone (ARRESTED) he alerted a network of friends and family to his situation.
Mercury News has the story.