I felt like I should chime in on this discussion, having been a cubmaster for almost 5 years. Yes, the den leaders report to the cubmaster. See the org chart:
http://www.scouting.org/scoutsource/CubScouts/Leaders/About/ThePack.aspx
I do agree that the CM should not micro-manage the Den leaders, but rather be a guiding hand. Pick good people and let them do their thing, guide them if they are off course, but allow creativity. I have den leaders not using the den leader planning guide despite making sure it is known to them. It has even come to the point of almost losing a leader, when
