  We show that neither accretion nor angular momentum extraction are likely to
lead to significant changes in the mass M_1 or angular momentum parameter a_*
of a black hole in a binary system with realistic parameters. Current values of
M_1 and a_* therefore probably reflect those at formation. We show further that
sufficiently energetic jet ejection powered by the black hole's rotational
energy can stabilize mass transfer in systems with large adverse mass ratios,
and even reduce the mass transfer rate to the point where the binary becomes
transient.
