The People scope in Central Administration was showing 0 ( zero ) items, but my Number of User Profiles in Manage Profile Services was showing plenty of profiles.

First I looked at the scope to make sure it was correct.

Scope Rule Type: Property Query

Property Query: urn:content-class:SPSPeople 

Behavior: Include

Next, I looked at the User Profile Service (Central Admin –> Manage Service Applications) or (http://yourCentalAdminURL/_admin/ServiceApplications.aspx).  I wanted to make sure the same account that was crawling all my data had access to this service.   Select the first User Profile Service item, then click on Administrators in the ribbon.  Your Default content access account should be listed here with Retrieve People Data for Search Crawls permissions.

If your Default content access account is not listed in the Administrators list, add the account and give it Retrieve People Data for Search Crawls permissions.

Where I can find my Default content access account?

Central Administration –> Manage service applications (under Application Management) –> click on Search Service Application.  There you should see your System Status web part, and listed will be Default content access account.