This "question" is biased because there is no definitive answer to this. The term "Open PC" is confusing: There's not such thing like "Open PC model" within the area of architecture/security models. 

> Users have full, system administrator/developer-level access to their own machine

From an IT Security/Administrator perspective that is obviously the worst thing to allow. One of the first rule of security is to perform an audit on the different roles within the organisation, define levels of permissions/access to the corporate assets & applications using the least privilege principle. Roles and permission must be rewied on a regular basis. Administrator accounts must be limited and strictly monitored.

The topic is broad, different aspects might be discussed:

 - Access Control model(s) to implement (MAC, RBAC, etc...)
 - Plaftform type (purpose built "appliances", dumb terminal, full PC,...)
 - OS architectures & limitations (Permission management, sandboxing, trust model...)
 - Software distribution (In house, SaaS, Classic vendor channel,
   "app-store"...)
 - Information System management