"I feel like eventually we're going to find out that black holes account for most of the dark matter out there, and just other mass in interstellar space that we have no means to detect"
Except that black holes are almost certainly not what physicists refer to as dark matter, they are (as far as we know) composed of 'normal' matter compressed by gravitational forces until collapsed into a singularity. As it is estimated that matter that we can't see makes up over 80% of the mass of the universe, if that mass was accounted for by black holes they would be far more common than stars (which they aren't, otherwise we'd see their effect on the movements of planets, stars and galaxies.)
Dark matter is so called because we can detect its gravitational effects, but it doesn't interact with normal matter other than through gravitational attraction, and it appears to be very diffuse (i.e. spread thoughout galaxies in lumpy clouds). You can't pick it up and weigh it, or have a look at it by illuminating it with a torch (flashlight for leftpondians), as it doesn't interact with either your hand or the light from your torch.
Biting the hand that feeds IT
