While my college days were pre-iPad, I have attempted to use an iPad as a note-taking device in continuing education courses and also for notes in general.
My advice? You will need a laptop to go along with it.
For short bursts of notes from meetings or the like, the iPad should be OK. If you get an external keyboard, it should be fine for taking notes in any situation, but unless you're really good at using the touchscreen keyboard (which is very easy to make mistakes on, especially if you're used to using physical keyboards), you should stick with the laptop.
One big advantage for students is that the iPad doesn't multitask as well. There's no hiding a webpage window aside your notes; by the time you switch from Safari to Pages, you've missed what you're going to write down, and you'll realize how dearly you pay for that early on.
The touch keyboard, more difficult editing (no mouse/trackpad), and more limited file management are what prohibit me from using my iPad more often. It mostly gets taken along when only small amounts of text are going to be entered. Everything else goes to a laptop.
For writing papers and larger assignments, a laptop is almost a necessity. Yes, it is possible to write the papers or complete the projects on an iPad, but you'll need lots of patience.
I do like my iPad for books. If you can get copies of the books you need on the iPad, it's worth it to have the iPad next to you while you use the laptop.
Calendars and other organizational tools are about equal.
We all know, of course, that you aren't going to be doing academics 24/7 at college. The iPad is the better entertainment machine--I use mine for Netflix, books, maybe an occasional round of the old SimCity Deluxe.
IF I WERE YOU...I'd get an iPad (larger size) and an 11" MacBook Air. A lot of people think the screen on the 11" is too small, but I've used two of them over the last five years and they've both been fine, even for producing page layout work (it's small but doable; of course, I was raised on 9" Mac Classic screens). Use them as a tandem and find what works best for you.
If money is an issue and you can only get one, however, the laptop is going to be a better fit for college overall if only for the ease of word processing.
Just wanted to point out that multi-tasking is coming this fall.