Motivated by the possible experimental opportunities to test quantum gravity via its effects on high-energy neutrinos propagating through space-time foam, we discuss how to incorporate spin structures in our D-brane description of gravitational recoil effects in vacuo. We also point to an interesting analogous condensed-matter system. We use a suitable supersymmetrization of the Born-Infeld action for excited D-brane gravitational backgrounds to argue that energetic fermions may travel slower than the low-energy velocity of light: delta c / c sim -E/M. It has been suggested that Gamma-Ray Bursters may emit pulses of neutrinos at energies approaching 10^{19} eV: these would be observable only if M gsim 10^{27} GeV.
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