At my organization we use TOPdesk as the service desk tool for all IT calls. We also use TOPdesk as our CMDB. TOPdesk is used only by the IT-department. Although we have looked into implementing TOPdesk for usage in another Department (our info desk) they decided to use another tool.
For the IT department TOPdesk fulfills it's role as a service desk tool and CMDB. We have all the businesses we support listed and their hardware in the CMDB. And hardware and user are linked.