I think a great place to look would be in Foucault as this is where Agamben (from whom I learned the term) gets it. He gives a fairly good account of it in an interview in 1978 with Le Bitoux (Mec, 1988, trans. Savran, 1992). The idea seems fairly similar to D&G’s discussion of the BwO – a zone of intensity, no longer a representation of an ontic being.
I am writing this week’s popOp about addictions (even masturbation, I guess) and the centrality of this concept to the very notion of how we think of the universe. I’m referencing, of course, Plato’s Phaedrus and the discussion of pharmakon–pharmakeia–pharmakeus-(pharmakos); thanks, Derrida!