  We study the consequences of the hadron-quark deconfinement phase transition
in stellar compact objects when finite size effects between the deconfined
quark phase and the hadronic phase are taken into account. We show that above a
threshold value of the central pressure (gravitational mass) a neutron star is
metastable to the decay (conversion) to a hybrid neutron star or to a strange
star. The "mean-life time" of the metastable configuration dramatically depends
on the value of the stellar central pressure. We explore the consequences of
the metastability of ``massive'' neutron stars and of the existence of stable
compact quark stars (hybrid neutron stars or strange stars) on the concept of
limiting mass of compact stars. We discuss the implications of our scenario on
the interpretation of the stellar mass and radius extracted from the spectra of
several X-ray compact sources. Finally, we show that our scenario implies, as a
natural consequence a two step-process which is able to explain the inferred
``delayed'' connection between supernova explosions and GRBs, giving also the
correct energy to power GRBs.
