  Recent theories of spin-current-induced magnetization reversal are formulated
in terms of a spin-mixing conductance $G^{mix}$. We evaluate $G^{mix}$ from
first-principles for a number of (dis)ordered interfaces between magnetic and
non-magnetic materials. In multi-terminal devices, the magnetization direction
of a one side of a tunnel junction or a ferromagnetic insulator can ideally be
switched with negligible charge current dissipation.
