The Ark of Truth (surprise, surprise, I'm a Stargate SG-1 fan), and contemplating the super-gate that is powered by a black hole that the Ori use to travel from their galaxy to ours and while traveling such a distance by an artificially produced wormhole may be something that is highly improbable, it did get me to thinking about the power of black holes and that maybe, just maybe, that is one place to go looking for aliens.
Let me explain. I am not saying black holes can be a natural habitat for some alien species. But black holes do give off immense energy. Not all matter that falls into a black hole is swallowed up, never to be seen again. No, a fair amount of it is given off by the matter as it is ripped apart before it gets to the event horizon (from which there is no return). Much of it streams out in a spiral along an axis.
Such unimaginable power sources just beg to be used / tapped into. OK, at least by species with similar outlook on power as humans. Some types of research may require incredible energies - our particle accelerators are but one example of this. Some explorations of our universe can only happen at high energies. And if some methods of interstellar travel, methods deemed impossible by us at the moment, like artificial wormholes, can only happen with great infusion of power, then black holes may be highly sought after. So maybe that's one place some aliens will not be able to resist, and so one place we may find them.
Of course, the aliens need to live somewhat nearby a black hole - close enough that even a very long journey is worth the effort and sacrifice (may be one way trips at first) to first get near one, study it, learn how to use it, and then invent and construct whatever device is needed to extract/capture the energy given off by in-falling matter. And what if other aliens have the same idea?
OK, so not very probable. But that's one of the fun things about speculation - don't need to stay only in the very probable.