Since gaining actual friends at college (I know, I know), I've been repeatedly surprised by how often people skip lecture. I must have noticed this earlier -- after all, I did observe that lecture halls tended to get less full as the semester went on -- but somehow I thought that all good students always went to lecture or some such. Apparently this is not the case.
Also, it seems like people are supposed to know by this time whether they're "visual learners" or "audio learners" or some such. I have never been able to figure this out. But apparently I learn pretty well by going to lectures (as opposed to doing the reading), although this is probably a motivation problem rather than anything else.
For 2.5 years this strategy served me well, but now that I run into courses with mediocre-to-poor lecturers who are always unclear and often omit large quantities of important material, it's becoming problematic.