  We study low-temperature nucleation in kinetic Ising models by analytical and
simulational methods, confirming the general result for the average metastable
lifetime, <tau> = A*exp(beta*Gamma) (beta = 1/kT) [E. Jordao Neves and R.H.
Schonmann, Commun. Math. Phys. 137, 209 (1991)]. Contrary to common belief, we
find that both A and Gamma depend significantly on the stochastic dynamic. In
particular, for a ``soft'' dynamic, in which the effects of the interactions
and the applied field factorize in the transition rates, Gamma does NOT simply
equal the energy barrier against nucleation, as it does for the standard
Glauber dynamic, which does not have this factorization property.
