I think it just depends on the school and the type of program you are applying to. Likely there are no hard and fast rules. Again, it's always wise to thoroughly investigate the schools you're interested in. Here's an interesting article from Hillsdale College about GPA's and grad school. In their experience, it has been an issue for some of their students. They claim that some medical and dental schools have an initial screening process that knocks out low test scores and GPA's in the first round. Maybe it's a "science" thing? I don't have any personal experience with it so I can't say for sure.
However, having gone through the experience of two kids applying to a variety of colleges and universities, we found that the larger universities have a very cookie-cutter approach to admissions. They didn't care what my son had accomplished (unless he happened to be a star athlete, of course). They only cared that he had completed the appropriate tests to their satisfaction and that I had created a beautiful, schoolish-looking transcript that was in their native bureaucratic language. Anything less gave them the vapors. One even required me to have my own signature notarized! I found many/most of them to be completely unable to think outside the box. Smaller, private schools, on the other hand, have a much more personalized admissions process and are looking for students who are well-rounded and will be successful at their schools. They actually have the time and will make the effort to look beyond the test scores and the GPA's.
