I and my co-workers have long hated the term “User”. It has a negative connotation in my mind. And many people have tried to come up with a catch all phrase to replace it. The answer is simple. Put a human face on your “User”.
Instead of saying: “The user logs onto the shopping web site”. Try this: “The shopper logs onto the web site”. This puts not only a human face on your use cases, activity diagrams and sequence diagrams it also adds context to the “user”. Think about these examples.
A user browses on Amazon.com or a shopper browses on Amazon.com
A user searches for information on MSDN or a developer searches for information on MSDN.
The user downloads forms from the HR portal or the employee downloads forms from the HR portal.
There is no "catch all" phrase so why not call users what they really are... people.