  Highly ionised winds with velocities ~ 0.1-0.2c were first detected in X-ray
spectra of non-BAL AGN a decade ago. Subsequent observations and archival
searches have shown such winds to be a common feature of luminous AGN,
increasing the belief that powerful ionised winds have a wider importance in
galaxy feedback models. Paradoxically, for the best-quantified high velocity
outflow (the luminous Seyfert PG1211+143) the wind appears too powerful to be
compatible with the observed stellar bulge and black hole masses, suggesting
the energy coupling of wind to bulge gas must be inefficient. A recent
XMM-Newton observation of the narrow line Seyfert NGC 4051 offers an
explanation of this apparent paradox, finding evidence for the fast ionised
wind to lose most of its kinetic energy after shocking against the ISM.
Importantly, the wind momentum is maintained through such a shock, supporting
the view that a momentum-driven flow provides the critical link between black
hole and stellar bulge masses implied by the observed M-sigma relationship.
