My sister-in-law is a high school teacher and has been wishing she could hook her iPad up to the projector since the day she got it.
Think of all the possibilities...makes so much more sense for a school to spend $500 on an ultralight, ultraportable iPad than spend more on bulky desktops you have to cart around just to play a video or show a web article (citation: my old high school).
There's not much more this feature lets me do on the app front, but man I'm excited to see what people do with it.