Nucleation and growth at defect sites is discussed in terms of rate equation models, which can be applied to metals deposited on oxide and halide surfaces. Strong trapping and rapid adatom diffusion is characterized by an extensive plateau, where the island density stays constant over a wide range of deposition parameters. Energies for defect trapping, adsorption, surface diffusion and pair binding are deduced for Pd deposited on Ar-cleaved MgO(0 0 1), which has recently been studied in situ by variable temperature atomic force microscopy (AFM). Calculations of these energies for Pd and Ag metals on both NaCl and MgO(0 0 1) surfaces are presented, and compared with earlier data for Ag, Au and Pd on NaCl.