As if life didn't come with enough to worry about the threat from black holes, even though they're thousands of light years away, is actually far greater than you think. Take A0620-00 for example, at 2,800 light years away it's not going to be sucking our planet into oblivion any time soon, but that doesn't mean it isn't a threat to life as we know it.
Not long after a star collapses into a black hole or if two stars collide, a huge amount of energy is released as a gamma ray burst and although our ozone layer protects the planet from gamma rays given off from the sun a full-blown gamma ray burst from a star collapse would pretty much fry earth. Even scarier still is that because they move at the speed of light we wouldn't see it coming.
The only sobering information is that for this to happen the gamma ray burst would have to be coming from somewhere inside our own galaxy which at present is highly unlikely.