My experience
I tried a semester-long experiment a couple years ago (with the first iPad). I used the iPad as my sole computing device. (English major, FYI.) There were some things that I loved about the iPad, some that I didn't. The form factor is a dream for school, as is the battery life, reading capability, etc.
As for notes, it sort of depends on your note taking style. If you are a concise note-taker, then it should be fine. My notes are all pretty much sentence fragments, so it worked. It wasn't as fast by any means. I did enjoy not having a screen between me and the professor; it's almost like having an open laptop creates a psychological barrier or something. I never got an external keyboard, because that seemed to defeat the purpose of the iPad's simplicity to me. I try to keep what I carry around to a minimum, and having two loose objects in my bag seems more complex than just carrying around a laptop.
Formatting pretty much sucks, and copy/pasting can be frustrating. With that being said, I was just barely thinking that I would probably buy the latest iPad if I had a couple semesters of school left. For me, the positives outweighed the negatives.