  Slow conductance relaxations are observable in a many condensed matter
systems. These are sometimes described as manifestations of a glassy phase. The
underlying mechanisms responsible for the slow dynamics are often due to
structural changes which modify the potential landscape experienced by the
charge-carriers and thus are reflected in the conductance. Sluggish conductance
dynamics may however originate from the interplay between electron-electron
interactions and quenched disorder. Examples for both scenarios and the
experimental features that should help to distinguish between them are shown
and discussed. In particular, it is suggested that the `memory-dip' observable
through field-effect measurements is a characteristic signature of the inherent
electron-glass provided it obeys certain conditions.
