Supervisor gets PhD student to do his entire job My master's supervisor delegates most (if not all) of his work to his senior PhD student. Let's name this student X. 


X creates all the assignments, midterms, and exams for the courses this professor is teaching (which is not in the TA job description)
He often fills in for this professor's office hours
In fact, this professor once got him to take his place and give a lecture on 10 minutes' notice
Anytime there is an administrative chore (such as ordering textbooks, arranging tests in the accessibility center, deciding whether to accept a student's excuse for missing a midterm, etc.) this professor always delegates it to X. 
X has written a significant portion of this professor's most recent grant proposal, even though X will not be part of the project.
I almost never see this professor; effectively, X has become my master's supervisor (this doesn't bother me, since I like working with X, but I'm sure he would rather focus on finishing his thesis).
Incidentally, a few weeks ago this professor also got me to update his CV to cover the last 6 years of his work. 


The list goes on, and also note that this professor also delegates the "usual things" to X, such as reviewing papers under the professor's name or making an appearance at certain events.

Is this type of thing acceptable (or at least borderline acceptable)? If not, how could I prevent it from happening to somebody else without making a scene? For bonus points, how could I improve X's situation?

Why does this matter to me? Because X will be graduating before me, and this professor is telling me that I will be taking over his duties (just as X took over the duties from the student before him). Although I obviously have the right to refuse anything unreasonable, this particular professor becomes very unhappy when anyone refuses something.
It is really hard to judge a case like this. It could be anything from a wonderful academic training situation to extreme abuse. It would depend on a lot of things not stated here. What is the agreement between X and the professor, now and for the future? What does the professor actually do with the time freed by X? Is it to X's benefit in any way - say via joint research? Does the professor have such a stellar academic reputation that anyone standing in his/her aura is bound to be a success. Or, such a stellar reputation that they can get away with abusing students without anyone complaining? 

If the professor treats the student like a colleague and they have agreed between them that the extra work will put the student into an excellent position for the future, then all is well. If the situation is delaying the student in some way, or impeding his/her research or future then it should be condemned. 

But if you are to step into such a role, you need to make sure that you agree to it and accept whatever tradeoffs there are. If they are to your benefit, then it would be worth considering, though not necessarily accepting. 

You should have a conversation with X to see what the long term view is. You should have a conversation with the professor to set appropriate limits and expectations. 

One of the extremes, of course is Stephen Hawking. His students were willing to do everything for him. Happy to do it. Thrilled to be there. Even when it was hard.