At a conservative estimate, I read around 1500 pages of college freshman writing a semester. I can't begin to calculate how many apostrophe errors I have seen. "It's" for "its" (and "its" for "it's") is annoying; by this point of the semester, I want to make it a capital offense; and, on occasion, it can be confusing. It's not the worst offense I see: poor organization, poor argumentation, poor research skills, poor critical reading and critical thinking skills are all much worse sins in a composition classroom. If a paper is exemplary in every way except apostrophe usage, I won't mark it down in any significant way. However, I've been on a week-long grading bender, and I'm feeling stabby.