  Sharp temporal decay estimates are established for the gradient and time
derivative of solutions to a viscous Hamilton-Jacobi equation as well the
associated Hamilton-Jacobi equation. Special care is given to the dependence of
the estimates on the viscosity. The initial condition being only continuous and
either bounded or non-negative. The main requirement on the Hamiltonians is
that it grows superlinearly or sublinearly at infinity, including in particular
H(r) = r^p for r non-negatif and p positif and different from 1.
