Casimir and van der Waals dispersive forces between real material surfaces can be strongly influenced by surface roughness and the frequency dependent dielectric functions of the interacting materials. The Lifshitz theory allows calculations of these forces between two flat plates if the frequency dependent dielectric function is known. Even in this case in order to compare different measurements of the Casimir force the accuracy must be higher than the force uncertainty arising as a result of the variation in the measured dielectric functions for a given material. Therefore, when we are dealing with dispersive forces between real materials, precise characterization of the particular interacting samples is critical. For this reason the effects of optical properties and surface roughness on dispersive forces will be first discussed in this review paper. Finally, we will compare research results among various research groups, at relatively large surface separations where roughness plays insignificant role, in order to show the level of consensus that has developed in this field in the recent years.