Some specific structures in which a growing quantity reaches record high values typically arise for instabilities in random media. Despite the rarity of these concentrations, they dominate the integral characteristics of the growing quantity (the mean value, the mean square value, etc.). The appearance of such structures is called ``intermittency''. The geometric properties of intermittent structures depend strongly on whether the growing quantity is a scalar or a vector. The scalar case is illustrated here by the example of an instability which arises in problems of chemical kinetics. The vector case is illustrated by the problem of the selfexcitation of a magnetic field in a random flow of a conducting fluid.