  A generic property of a first-order phase transition in equilibrium, and in
the limit of large entropy per unit of conserved charge, is the smallness of
the isentropic speed of sound in the ``mixed phase''. A specific prediction is
that this should lead to a non-isotropic momentum distribution of nucleons in
the reaction plane (for energies around 40 AGeV in our model calculation). On
the other hand, we show that from present effective theories for low-energy QCD
one does not expect the thermal transition rate between various states of the
effective potential to be much larger than the expansion rate, questioning the
applicability of the idealized Maxwell/Gibbs construction. Experimental data
could soon provide essential information on the dynamics of the phase
transition.
