Hi Marshall,

you can use WPMU to develop your site, but if you are more familiar with Wordpress you can achieve the same result with multiple single installations. You need to separate the blogs because in this way you can use the basic wordpress user roles & permission system.

You could assign the author role to the majority of the people of the company, and the editor role to the head of each division. So each blog will have 1 editor and N authors.

Authors can only access and edit their posts. Editors can access and edit all the information.

If you need a more granular control over the permissions you could customize the capabilities of new roles.

Here you can read some useful info and find some plugins at the bottom:
http://codex.wordpress.org/Roles_and_Capabilities

Each user in Wordpress have his personal info in the User Panel. If you need more fields or you need to store more complex information you could use a specific per-user page tagged in some way or put in a given category.

I think you can do it. Using categories, custom fields and tags it's possible to create very complex information architectures.

You can easily retrieve content from all your single users or you can merge their contributions if the content relate to a dvision.

I hope this will help