  We show that the generalized second law of thermodynamics may shed much light
on the mysterious Kovtun-Son-Starinets (KSS) bound on the ratio of viscosity to
entropy density. In particular, we obtain the lower bound $\eta/s
+O(\eta^3/s^3)\geq 1/4\pi$. Furthermore, for conformal field theories we obtain
a new fundamental bound on the value of the relaxation coefficient $\tau_{\pi}$
of causal hydrodynamics, which has been the focus of much recent attention:
$(\tau_{\pi}T)^2\geq {{(\sqrt{3}-1)}/{2\pi^2}}$.
