  Extending previous results [Phys. Rev. Lett. 97, 081301 (2006)], we explore
the cosmological implications of a new quintessence scenario driven by a slow
rolling homogeneous scalar field whose equation of state behaved as freezing
over the entire cosmic evolution, is approaching -1 today, but will become
thawing in the near future, thereby driving the Universe to an eternal
deceleration. We argue that such a mixed behavior, named \emph{hybrid}, may
reconcile the slight preference of current observational data for freezing
potentials with the impossibility of defining observables in the
String/M-theory context due to the existence of a cosmological event horizon in
asymptotically de Sitter universes as, e.g., pure freezing scenarios.
