I use my iPad for almost everything I do these days. I teach with it wirelessly using an AppleTV that IT has installed in every classroom. I read and annotate PDFs with it. I have students submit assignments as PDFs and then read them, mark-them-up, and email them the PDF back. I take notes with it exclusively (meetings, research, etc..).
Click here for a video where I talk about some ways to teach/lecture with an iPad.
Click here for my page of iOS App and Hardware reviews reviews.