Observations of mechanical feedback ranging from individual stellar wind bubbles to galactic superwinds are all largely consistent with the conventional adiabatic model for shell evolution. Presently none of the discrepancies are of a magnitude that suggest any need for major revision of the conventional understanding. The existence and properties of multiphase gas and filamentary structure are broadly consistent with the adiabatic model. It is also a remarkable strength that the model succeeds across size scales ranging over at least three orders of magnitude.
However, characterizing the dominant parameters and their effects on the shell evolution is still highly problematic. For example, critical ambient ISM conditions like density, pressure, and ionization distributions remain elusive. The mechanisms and conditions for cooling of the interior energy need to be identified, and energy budgets reliably determined. Perhaps the most fundamental question is the fate of the hot gas generated within the superbubbles: Does it escape to constitute the HIM? Does it escape from starburst galaxies, and from their gravitational potentials? These issues have crucial consequences for galactic evolutionary processes, and our understanding depends on further clarifying the mechanical feedback process.
I gratefully acknowledge support from the WS-ISM session organizers.