  I review the progress made on the physics of relativistic jets from black
hole systems in the context of the analogy between AGN and microquasars that
was proposed one decade ago. If the emerging empirical correlations between the
observational properties of stellar and supermassive black holes will become
more robust, we will use them to determine the mass and spin of black holes,
independently of theoretical models. Microquasars are fossils of sources of
Gamma-ray bursts (GRBs) of long duration, and their kinematics provides
observational clues on the physics of collapsars. If jets in GRBs, microquasars
and AGN are due to a unique universal magnetohydrodynamic mechanism, synergy
between the research on these three different classes of cosmic objects will
lead to further progress in black hole physics and astrophysics.
