  The relation between rotating plane Couette and Taylor-Couette flows is
clarified. The identity of their linear stability limits is explained by
considering the effect of the Coriolis force in the rotating frame.
Experimental data are used to quantify the behavior of the minimum Reynolds
number for subcritical turbulence as a function of rotation and curvature. This
last dependence is understood through a phenomenological analysis, which also
implies that the Coriolis force reduces the efficiency of subcritical turbulent
transport with respect to nonrotating flows, as observed numerically.
