How safe is the land of the free?

The order of magnitude speaks for itself: three dead in Boston, nearly 3,000 in New York City. Still, in the aftermath of the Boston tragedy, it is impossible not to ask the same questions that came on the heels of 9/11: just how safe are Americans in their homes, in their workplaces, on their streets, and at their celebrations? And just how safe can they be?
At time of typing, the two brothers, ethnic Chechens from Russia, suspected of bombing the Boston Marathon seem to have been motivated by a radical brand of Islam but are not connected to any Muslim terrorist groups. Dzhokhar Tsarnaev has been charged with crimes which could bring the death penalty.