Copycense points us to a story by English professor, James Lang, who notes that many universities and professors say that it's unethical or against school rules for students to reuse papers for multiple courses, but the more he thinks about it, the more he wonders why this is wrong, noting that professors do this all the time, reusing papers, presentations, research and lesson plans. Even if the idea is that students are supposed to "do work," it's not clear that there's anything wrong with a student reusing a paper, as long as it suffices for the assignment:

But--practically speaking--the opportunity to reuse a paper might arise only once or twice in a student's career, thanks to the diversity of our course assignments and disciplines. A paper assignment that a student gets in my English class on 20th-century literature won't be anything like her assignment in Renaissance literature--much less from psychology or sociology. Because the content of courses differs so much, the opportunity to use the same paper will happen only rarely.

But when it does, why not allow a student to take advantage of the opportunity? Suppose a student writes a final research paper for an introductory psychology course in the fall semester of her freshman year, and receives helpful suggestions on it from the professor. That same student then takes an English-composition course with me in the spring, and I assign an open-topic research paper to finish the semester.

Why should I not encourage the student to revise her psychology paper, according to both the guidance she received from her previous professor and the new writing principles she has learned in my course? She couldn't merely turn in her old paper; it would have to fulfill the requirements of my assignment. The student would not only get the opportunity to return to a set of ideas she thought she had finished, but the assignment would also reinforce the interdisciplinary nature of knowledge and the curriculum.

The article is based around the question of whether it's okay to "plagiarize yourself," but I worry that even that's a bit misleading. You can't plagiarize yourself. Plagiarism is about passing off someone else's work as your own. Reusing work is not the same thing at all, but is a separate issue -- and one that doesn't really seem to be much of a problem once you think about it.