In "Snowclones are the dark matter of journalism", 1/24/2004, I noted the spread of the phrasal template X is the dark matter of Y: "The PC is the Dark Matter of the Internet", "Global technoscience is the dark matter of social theory", "Networking is the dark matter of high-speed internet", "Terrorism is the dark matter of the civilized world", "The extraterrestrial hypothesis is the dark matter of political science and science policy in the second half of the twentieth century", "Euroscepticism is the 'dark matter' of German politics", "the Boswell Co. now stands revealed for what it is: the dark matter of 20th century California history", "Intellectual property is the “dark matter” of the corporate universe".
A search today, almost seven years later, would turn up many more: "Untested code is the dark matter of software", "Influence is the Dark Matter of the Social Media Universe", "Organized crime is the dark matter of Ohio politics", and so on. And just this morning, I learned that dark matter has at least one scientific sense outside of physics.
According to Philipp Kapranov et al., "The majority of total nuclear-encoded non-ribosomal RNA in a human cell is 'dark matter' un-annotated RNA", BMC Biology 12/21/2010:
We show that the relative mass of RNA whose function and/or structure we do not understand (the so called 'dark matter' RNAs), as a proportion of all non-ribosomal, non-mitochondrial human RNA (mt-RNA), can be greater than that of protein-encoding transcripts.
I just learned about this usage today, but if I'd been paying attention, I'd have picked it up a lot earlier, as the "so-called" in the quoted sentence hints. Thus Jason M. Johnson et al., "Dark matter in the genome: evidence of widespread transcription detected by microarray tiling experiments", Trends in Genetics 21(2):93-102, February 2005: "Recent ‘tiling’ microarray experiments that assay transcription at regular intervals throughout the genome have shown evidence of large amounts of transcription outside the boundaries of known genes."