We present experimental results on magnetization reversal for a class of nanoscale magnetic films with perpendicular magnetic anistropy and develop a model that describes a variety of related experiments. In this model the sample is divided into identical single domain cells that interact through dipolar fields and a nearest-neighbor domain-wall interaction. Monte Carlo simulations give insights into the relationship between macroscopic magnetic parameters and the reversal behavior and demonstrate the important role that thermal activation plays in the reversal process.