I think it depends a lot on the school or the department.
When I was in grad school for physics, C+ was considered failing. Beyond that, we were specifically told, as long as we passed, grades didn't matter. It was of course quality of research that mattered.
I don't know how differently people faired with different GPA's coming out. I think employers mostly looked at publications and references. And I'm not far enough out to say who was "successful" yet.
The first CS department I was in didn't have quals. You had to maintain a 3.7 GPA over all course work to be admitted as a Ph.D. candidate, so grades did matter.
I wish I had started out in departments like some of you described. I started doing research my first year, and my grades suffered for it. I got three of those Bs, and I had to take an extra course just to be admitted as a Ph.D. candidate in that program. Luckily, I have since transferred to a different school.
When I was in grad school for physics, C+ was considered failing. Beyond that, we were specifically told, as long as we passed, grades didn't matter. It was of course quality of research that mattered.
I don't know how differently people faired with different GPA's coming out. I think employers mostly looked at publications and references. And I'm not far enough out to say who was "successful" yet.