As a teacher on break, I'm looking forward to getting back and trying to use the iPad as a replacement for my current cumbersome setup of netbook/graphics tablet/projector. I've been using that setup for classroom notes, diagrams, etc - basically, anything I once would have written/drawn on the whiteboard.
The beauty of such a setup is that you have a record of what you've done in class, plus the ability to email that information to anyone who is interested.
I love the idea of the iPad's instant-on, it's portability and the fact that you can write/draw straight onto the screen (much easier than using a graphics tablet).
But which app(s) to use for such a purpose? The thing you've got to keep in mind with the iPad is that not all apps have VGA-out capability (eg, Safari!!).
The VGA-capable note-taking apps that I've been investigating as whiteboard replacements are Penultimate, Noterize and Note Taker HD. All have different strengths and weaknesses that I'm happy to go into if anyone is interested.*