Bag of Hurt
DRM getting out of hands again: imagine the poor schoolteacher's shock when his new aluminum MacBook refused to play a movie he bought from the iTunes Store because a "a display that is not authorized to play protected movies" was connected.
The technology is called HDCP - High-bandwidth Digital Content Protection - and its main purpose is to protect digital content traveling through various high definition capable display ports from being copied. In this case it also prevented the teacher from showing a movie to his class on a projector.
Arguably a presentation of a movie to a classroom of kids stretches Fair Use or Private Viewing, and I don't know what the relevant US laws say. But still I think that if any DRM causes this kind of frustration to the rightful owners of the content, then it is flawed, and very much so.
Also if we assume that the exact same thing could happen to anyone who would want to watch a perfectly legally obtained HD movie at home, it's hard to argue that the protection used is effective. (In the teacher's case the Mini DisplayPort - VGA adapter caused the error.) Rightful owners should not be treated like criminals.
Commenters pointed out that the incorporation of the HDCP technology is probably the price Apple had to pay for getting a permission to put BluRay devices in future Macs. Also, since Apple is in the unique position of offering a download-and-carry model with the iTunes Store - meaning the customers will have a fully assembled movie file on their end when buying content - the licensors can play all kinds of hardball games with Apple in exchange for letting their content in.