The iPad is great as a mobile computer and almost great for note taking.
The only problem I found with it is if you are in an economics class and require symbols (, ), $, #, etc. you will be tapping lots to alternate to the symbol keyboard. You should probably buy the keyboard dock with it. I'd also recommend a stand so you can prop it up.
There are LOTS of apps out there for ink note taking, there are also apps for hybrid note taking (ink and text).
With that being said, you say full essays, I wouldn't type a full essay on the iPad keyboard, you'd need the docked version for that.
I switched back to my MacBook Pro for notes, primarily because of the need to be pressing the symbol key to switch to the symbol keyboard and I have a tablet built in to the MacBook Pro (using Inklet).
If you go with the iPad you want this Stylus:
http://tenonedesign.com/sketch.php