  We construct a unified semiclassical theory of charge and spin transport in
chaotic ballistic and disordered diffusive mesoscopic systems with spin-orbit
interaction. Neglecting dynamic effects of spin-orbit interaction, we reproduce
the random matrix theory results that the spin conductance fluctuates
universally around zero average. Incorporating these effects in the theory, we
show that geometric correlations generate finite average spin conductances, but
that they do not affect the charge conductance to leading order. The theory,
which is confirmed by numerical transport calculations, allows us to
investigate the entire range from the weak to the previously unexplored strong
spin-orbit regime, where the spin rotation time is shorter than the momentum
relaxation time.
