Considering that I work in the PC Deployment office at my university, I know that we are getting more and more Macs in each day that departments are purchasing, but most instructors do not use a laptop in class. So far, I have had NO Mac users for an instructor but I know some that I have not had a class with that use them in their offices. It's becoming closer to 10 percent for my university and growing.
Now, student body-wise, it's probably closer to 30-40 percent.