The thing which stopped the worst abuses of power against the people was the presence of the global media in countries where the west had significant financial and political interests.
The broad sweep of technology available these days (from reporters with satellite phones to twitter, to the ability anyone has to send photos across the world in seconds) may present future genocides, but Twitter and Facebook are just one small part of the picture.
But does anyone believe that Twitter would have stopped Darfur? People know what's happening there and it's still happening so I'm dubious as to how a communication tool would have changed that.