Nanocomposite thin film structures are presently being studied because of their interesting nonlinear optical properties. The microstructure of plasma-deposited nanocomposite films consisting of gold particles embedded in a plasma-polymerized fluorocarbon matrix was fully characterized using a generalized Maxwell-Garnett effective medium approach applied to ellipsometric data. The particle size dependence of the dielectric properties of gold was treated classically using a broadening parameter, A, equal to 0.25, as determined from transmission electron microscopy analysis. In general, the model predicted correctly the dependence of microstructural characteristics on glow discharge parameters and post-deposition thermal treatments. However, careful interpretation of the model fit parameters is necessary in both the high gold volume fraction limit and small particle size limit. For the former, misleading results with respect to particle size and shape may be obtained due to aggregation effects, the onset of which was determined to occur at a gold volume fraction of about 30%. For the latter, deviations from the classical description of the permittivity of gold nanoparticles (occurring for particles smaller than 7 nm) can lead to misleading results with respect to particle shape.