it depends a lot on the professor. also, I don't know how many other schools do it this way, but USC grades using a 4.0 scale using all the tenths. So, for example, you can get a 3.5, a 3.6, a 3.7, a 3.8, etc. I think this tends to make the spread tighter than if regular A,A-,B+, etc. grades were used.
But just to give you something to look at, in my classes for the spring semester: 4 out of 65 in my con law class got a 3.8 and up (6%), 5 out of 53 in my crim law got 3.8s and up (9%), 5 out of 63 in my ethics class got 3.8s and up (8%), 6 out of 62 (10%). My school's median is a 3.2, and somewhere I heard that about 20% of students end up getting an A at some point in their first year.