Most of the recently discovered superconductors, like all cuprates, MgB2, or NaxCoO2?nH2O, are uniaxial crystals with metallic ab planes orthogonal to an insulating, or sometimes poorly conducting, c axis. The reflectivity Rab(omega) provides, through the optical conductivity sigmaab(omega), valuable information on the low-energy electrodynamics of these intriguing materials. However, in the far infrared, Rab(omega) ~ or = 1 and a slight contamination from the c-axis response or an unsuitable choice of the extrapolation to omega=0 may lead to large errors on sigmaab(omega). These issues are quantitatively discussed here with particular regard to La2?xSrxCuO4+y, one of the most-studied high-Tc materials.