A good brief sumamry in the form of a book review, from Science and Society 72, 4 (2008)
"'Monetary theory of value' usually evokes, in German speaking countries, an approach to Marx that has developed out of the work of Hans-Georg Backhaus over the last thirty years or so; its guiding assumption is that the Marxist theory of value 'is conceived as a critique of pre-monetary theories of value' and 'is essentially a theory of money at the level of the description of simple circulation' (Backhaus 1997, 94). In the past few years, Michael Heinrich, above all, has taken up the cudgels for Backhaus' thesis.
"Heinrich takes issue with the idea, still frequently encountered in the ongoing discussion of Marx's theory, that money is merely a formal translation of an immanent quantity of value:[Money] is, rather, the necessary, and, above all, 'only possible form in which the value of a commodity can appear'. There can be no form in which value is manifested independently of exchange, for to admit this implies abolition of the difference between privately expended and socially recognized labour. (Heinrich 1999, 242)"
Full article as PDF: http://halshs.archives-ouvertes.fr/docs/00/42/26/20/PDF/Hoff_Kritik_der_klassischen_politischen_Okonomie-Science_Society.pdf