Most static mixers are designed to maximize radial mixing to achieve compositional and thermal homogeneity. Flow inverters maximize heat transfer. Axial mixers that closely approximate an exponential distribution of residence times have been devised as well. More recent papers describe static mixers for surge dampening in industrial swing-cycle processes. An extension of this result allows complete attenuation of surges even when the component with periodic concentration variations is reacting by first order kinetics. Another class of motionless mixer is intended to maximize first appearance times in laminar flow, tubular reactors. Coiled tubes, especially with periodic changes in the direction of the principle axis have shown excellent results but are somewhat cumbersome in terms of spatial layout. Baffles in a short, fat reactor used for sterilization have been shown effective. The general question is: what objectives functions are reasonable for static mixers and how can near optimal performance be achieved in practical hardware? The first question is addressed using the tools of residence time theory. The second question is usually addressed using commercial CFD packages, but valuable insights can be provided by simple, transparent code. New results, limitations and occasional frustrations are discussed.