  15 years of XMM-Newton observations have established that ultra-fast, highly
ionized winds are common in radio-quiet AGN. A simple theory of
Eddington-limited accretion correctly predicts the typical velocity (~0.1c) and
high ionization of such winds, with observed flow energy capable of ejecting
star-forming gas. With a recent extended XMM-Newton observation of the
archetypal UFO, PG1211+143, revealing a more complex flow pattern, we suggest
that targetted observations over the next decade offer unique potential for
probing the inner accretion disc structure and SMBH growth.
