Business Units are the way to reproduce the hierarchy of an
organization within MSCRM - under your top-level BU you can create a
number of tiers and manage access by allocating different scope roles
(global, BU, team, self) to different users. However you may well have
to create new custom roles, depending on how the functions operate
across the BUs. You will probably also need to enhance the standard
reporting to provide breakdowns and rollups over the BU tiers. If it's
a very large organization you could also consider multi-tenanting.
Chris
http://mscrm4u.blogspot.com