  This is a write-up of a talk given at the Opava RAGtime meeting in 2011, but
it has been updated to include some subsequent related developments. The talk
focused on discussion of some aspects of black hole and cosmological horizons
under rather general circumstances, and on two different topics related to
formation of cosmological structures at different epochs of the universe:
virialization of cold dark matter during standard structure formation in the
matter-dominated era, and primordial black hole formation during the radiative
era.
