^^^Good question, Defiance. A quick search for "what happens when black holes merge" brought up a couple of links to start with:http://www.universetoday.com/97686/what-happens-when-supermassive-black-holes-merge/http://io9.com/5525150/what-happens-when-black-holes-combine
One thing that's essential to keep in mind is that black holes aren't solid or plasma, like planets or stars. They're points of nearly inconceivable density: hundreds, sometimes millions of solar masses compressed by their own gravity into tiny (for their mass) volumes. The interaction of the magnetic fields and accretion discs (the infalling matter orbiting the holes) of such objects is much more dramatic and detectable, as the articles point out, than the merger of the black holes themselves.
It isn't clear what you mean by "poof", but the models and observations show that merging singularities make the immediate neighborhood (out to quite a distance, if they're galactic-core sized) very
unhealthy for life as we know it. Lots of hard radiation and heat emitted by the colliding accretion discs, tidal forces from the nearing singularities... Yow.
Something best admired and studied at a safe distance, to be sure.