  It is the twentieth anniversary of the publication of the seminal papers by
Magorrian et al. and Silk & Rees which, along with other related work, ignited
an explosion of publications connecting active galactic nuclei (AGN)-driven
outflows to galaxy evolution. With a surge in observations of AGN outflows,
studies are attempting to directly test AGN feedback models using the outflow
properties. With a focus on outflows traced by optical and CO emission lines,
we discuss significant challenges which greatly complicate this task from both
an observational and theoretical perspective. We highlight observational
uncertainties involved, and the assumptions required, when deriving kinetic
coupling efficiencies (i.e., outflow kinetic power as a fraction of AGN
luminosity) from typical observations. Based on recent models we demonstrate
that extreme caution should taken when comparing observationally-derived
kinetic coupling efficiencies to coupling efficiencies from fiducial feedback
models.
