(1) interaction of molecular diffusion with simple unidirectional shear flows (bounded and unbounded domains). (2) Limitation of the effective diffusion approximation to long times and small domains, and low moments of the tracer distribution. (3) Perhaps a geophysical example: shear diffusion in the internal gravity wave field. The vertical tracer cascade of Haynes & Anglade. (4) Some examples of "pre-asymptotic" anomalous shear diffusion e.g.,〈x2〉 ∼ t ln t due to the no-slip condition, and 〈x2〉 ∼ t 3/2 in the example of de Marsily & Matheron.