While this seems like a good idea on paper (oops, pun), it's really not, unless you can afford 2 iPads.
The reason? Studying or doing homework with a textbook typically involves at least two surfaces -- 1 surface from which to read, and 1 surface on which to write. Multitasking between 2 apps could potentially improve your short-term memory, since you'd have to constantly go back and forth, but it would not be my method of choice.
If you are really set on going paperless, I'd by an MBA (for portability) but always have access to a second monitor so that I can read from one screen and write onto another screen. Of course, you'd lose a lot in terms of handwritten diagrams, etc that you may need to do your homework. So, best bet would be an MBA + iPad I suppose. But that's a lot of money for very little benefit..
Some other random thoughts.
- Paper is also recyclable, so, environmentally it's not as bad as we make it out to be.
- I've always remembered things better when I've physically written something on paper than when I typed my notes on computers.
- If you are in high school, I'd rather spend my energies on upping grades rather than experimenting with different input/tech methods. But maybe that's just me.