I taught an entry-level math course in the fall of 2010. Although I had no attendance policy, most students attended regularly (not perfectly, but regularly) throughout the semester. A significant minority had spotty attendance for at least part of the semester, and often only a small part. Take a look at the grade distribution for the class:
I guess that the lesson here is to be responsible in at least two ways. While my previous teaching experience shows that this is not a guarantee of success, the charts above suggest that responsibility might not be too bad of an idea.