In case you missed it, Sunday's SF Chronicle had a good commentary on what it takes to teach writing...which usually includes a lot of time spent reading, correcting and commenting on student papers (that's the purple pen part...I've decided purple pen marks are nicer and a tad less strident than red ones).
The commentary, "The Goal is Garbage In, Writers Out," also contains some seriously entertaining examples of mistakes you don't want to make. See how quickly you can spot the errors.
While I agree with the author's approach to grading papers, I wouldn't call most student papers "garbage." Actually, most are pretty good, and some are really good. And all it takes is one or two really good ones to make my day.
So, please...make my day!