Paints are complex materials composed of polymers (binders) dissolved in one or more solvents, pigments, and other additives. The thermodynamics of such systems is essential, for example, for selecting improved solvents and understanding a number of phenomena related especially to adhesion to solid surfaces and drying. Many engineering models have been applied over the last decades for solutions with commoditity polymers. In this work, the performance of some of these models is investigated for paint-related systems, focusing on those drying by the so-called “lacquer mechanism” (evaporation of solvents). These are the Entropic-FV, UNIFAC-FV, GC-Flory, and the Flory-Huggins models using various ways for estimating the FH parameter via solubility parameters. Achievements and shortcomings of these models are discussed in conjunction with difficulties encountered in such calculations. We conclude that, despite the uncertainties involved, several models yield reasonably accurate activity coefficients, even at infinite dilution. Thus, engineering models may be useful for solvent selection via semiempirical rules of thumb, which are based on thermodynamic considerations.