What to do about fellow student that hogs lecture time with many questions I am in a master's program, and one of my peers in the program is in two classes with me. He is a nice person, but he tends to ask a lot of questions in lectures; both of which are very large, and often ends up derailing the lecture for 25-30 minutes.

It has (long since) gotten to the point where many people are bothered by it. He will ask a question if he is hazy on any details, and often doesn't allow us to cover all of the material in a lecture because of it. In addition, the professor is typically forced to just repeat him/herself, so we don't even learn anything new from his questions. Of course, we are still responsible for that material regardless of whether it is covered lecture. The professors appear to be bothered by his behavior, though I wouldn't presume to know for sure.

Can and should I say something to this person? I don't want to discourage him from asking questions or feel disliked by his peers in the program, but it seems unreasonable to allow him to negatively affect my and other students' learning experience (and to a rather severe degree).

Note that I am aware of this post detailing how to handle disruptive questions, but I think my question is different because it concerns how to handle it from the perspective of a fellow student rather than a professor.
Unless this student is a close friend of yours, I think you should bring it up with the course instructors, not directly with him.  The person who is in charge of making sure the course is operating smoothly and well is the instructor.  In a class with more than a few students, spending 25-30 minutes responding solely to one student sounds like a clear mistake to me.  (The fact that this is happening in multiple classes and none of the instructors have done anything about it is curious to me, but I don't really know what to make of it.)

I would make an appointment to speak to each instructor in question about it.  I would come to that appointment with specific information about other students who feel the same way.  If we are talking about a few students, then probably you should come to the office together.  I am a university professor, and if several students came jointly to my office to express concern about the way my class was run, I would have to take that very seriously.  

If the number of students who are concerned about this is more than could comfortably fit in your instructor's office, then I think you should make a list of such students in some way, e.g. by writing up a brief, politely worded statement describing your feelings on the situation and getting other students to sign it.  Or perhaps even in the second situation it might be better to start with a few students who come visit your instructor's office.  Things to worry about in the second situation are (i) you don't want to attribute a complaint to a classmate unless you have specifically talked to them about it and gotten their approval and (ii) if you don't handle things with enough discretion it could get back to your inquisitive peer in a way that you don't want.

Perhaps others will disagree, but I really do feel that if the behavior is acceptable to the course instructors then it has to be grudgingly acceptable to you: I would not try to persuade your peer to change his ways.  If the additional time spent on your inquisitive peer has consequences in terms of the learning experience, you should bring those consequences to the attention of the instructor, specifically and repeatedly if need be.  For instance, if the lectures do not cover all the material that the syllabus says they should, you could ask the instructor what to do about that and whether the exams will be adjusted accordingly.  (This is a pointed, but fair, question.)  If at the end of the course it turns out that indeed the learning experience was compromised in this way, then you should give appropriate feedback about it.  

The only case I can think of in which I would confront your peer directly is if you have as much discussion with the instructor(s) as you can, they agree that the questions are derailing the lectures but are themselves unwilling to do anything in response.  They are then really not doing their job, and I think at that point you would be justified in trying to intervene: it seems like the least evil.