Every quarter a number of students ask me, hopefully, if my class is graded on a curve. These students cling to a belief that a curve will somehow help their performance in class. This naive faith is as misguided as the belief that they can successfully absorb a lecture while texting and listening to an iPod. So, I patiently explain that a curve makes their grade dependent upon everybody elses, that it means that their grade communicates nothing about their understanding of the subject, and that the middle of the curve is really and truly a "C". I tell them that they should not want a curve, and that curves are intrinsically evil.
Here's another prop for my argument. It's an article from the NY Times about law schools that hand out lots of merit scholarships, but because they grade on curves, it is mathematically impossible for the majority of the scholarship students to maintain good enough grades to keep their funding. Pretty skanky on the part of the law school, and another reminder that grade curves are intrinsically evil.