I absolutely agree with Anders on this ... no question should be off limits if you are just trying to find out what the deal is about the job, the conditions, and your remuneration ... in fact I think it is a joke to say otherwise

When I go for a job, yes I am trying to sell myself, but I am also asking myself the whole time "are these guys worthy of employing me", and way more than once I have walked out on an interview, either because they would not reveal such information, or because they were misleading or deceptive in the way it was presented (and if I had know the truth I would never have come to the interview in the first place), or some other similar reason.

There are plenty of dodgy employers out there, and if you DON'T ask these kinds of questions, then you are really taking a huge risk with your career.