Nucleation phenomena are very important in nature because they control the formation of novel phases which can have technologically important properties and applications. LEEM experiments in real time are described for island nucleation in Pb/Si(1 1 1), that show unusually fast, defect-free large Pb islands. The experiments confirm that this growth is due to the collective motion of the wetting layer and provide real time information about the rate of mass transport. Review of other experimental systems where similar unusually fast nucleation processes are present can lead to a better understanding of these intriguing processes, so predictability of the growth conditions (temperature, flux rate, coverage) can be attained.