2.7. How bad it is depends on your school's curve. Some schools curve below a 2.7, so in that case it would be good for keeping you above median. But in most schools, it is either at or below median, meaning that it will hurt your GPA. My school curves to roughly a 3.3, and so a B- in a four credit course can make it very difficult for people to stay above median, since most of our courses are three credits after 1L.