  For gauge theories with an Einstein gravity dual, the AdS/CFT correspondence
predicts a universal value for the ratio of the shear viscosity to the entropy
density, $\eta/s=1/4\pi$. The holographic calculations have motivated the
formulation of the celebrated KSS conjecture, according to which all fluids
conform to the lower bound $\eta/s \geq 1/4\pi$. The bound on $\eta/s$ may be
regarded as a lower bound on the {\it relaxation} properties of perturbed
fluids and it has been the focus of much recent attention. In particular, it
was argued that for a class of field theories with Gauss-Bonnet gravity dual,
the shear viscosity to entropy density ratio, $\eta/s$, could violate the
conjectured KSS bound. In the present paper we argue that the proposed
violations of the KSS bound are strongly constrained by Bekenstein's
generalized second law (GSL) of thermodynamics. In particular, it is shown that
physical consistency of the Gauss-Bonnet theory with the GSL requires its
coupling constant to be bounded by $\lambda_{GB}\lesssim 0.063$. We further
argue that the genuine physical bound on the relaxation properties of
physically consistent fluids is $\Im\omega(k>2\pi T)>\pi T$, where $\omega$ and
$k$ are respectively the proper frequency and the wavenumber of a perturbation
mode in the fluid.
