But the web client hasn't been updated to do real "on-behalf-of" calendar sharing yet. Please check out bug 10652 in bugzilla and vote if you'd like this issue prioritized!
One of the departments where I work is a legal clinic.
There is a Lawyer Coordinator
An Admin Asst.
Student Lawyers who meet clients
I did the following:
1. I have a shared calendar that the Admin Asst has access to.
2. She books appointments for the student lawywers by scheduling meetings with them and making the "organizer" the shared calendar which she generally leaves unchecked.
The benefits are:
-that there is a master calendar with every appointment viewable to the Admin asst, but she keeps hidden most of the time
-the student lawyers have their own non-cluttered calendars with just their appointments
-they all get invitations that they need to accept indicating they've really acknowledged the appointment
3. Furthermore, I am going to start asking the Admin Asst. to include the email address of the client in the invitee list so the clients get an email too.