At just over a year old, Facebook Safety Check was originally trumpeted as a tool for natural disasters. The use of it during a terrorist attack as vast as this still only appears to be is a natural evolution of the product.
The only drawback to this toolset is it seems to depend on Facebook for deployment. I would really like to see the set of criteria an event needs to meet in order for it to be activated. I think that the other social networks would benefit from developing either similar systems or… and here’s a novel idea… maybe they could all work together on one “I’m Safe” check-in system.