We argue, for a wide class of systems including graphene, that in the low
temperature, high density, large separation and strong screening limits the
drag resistivity behaves as d^{-4}, where d is the separation between the two
layers. The results are independent of the energy dispersion relation, the
dependence on momentum of the transport time, and the wave function structure
factors. We discuss how a correct treatment of the electron-electron
interactions in an inhomogeneous dielectric background changes the theoretical
analysis of the experimental drag results of Ref. [1]. We find that a
quantitative understanding of the available experimental data [1] for drag in
graphene is lacking.Comment: http://iopscience.iop.org/0953-8984/24/33/335602