I suppose that I use other terms when I am talking about the people who use a specific application. So I might refer to them as "the Architect" if it is an architects application, and will often want to distinguish between, say, architects and secretaries, and so would use appropriate terms for the types of users.

Having working on e-commerce sites, I try to distinguish between "clients" - the people paying us to build the site - and the "customers" who are the people who will use the site at the far end.

This is probably a better approach than just considering them all as "users", because it distinguishes between different types of people using the system. It means that the different types of user can be distinguished, and addressed in different ways - all types of user are not hte same.