<p>I use a 12 inch ibook and love it because its light and mobile, in my classes where there are a lot of people it doesn't take up any room.</p>
<p>Keep in mind I had spent most of my time using dual 19 inch monitors because I did a lot of design work, but it only took me a day or so to really switch to 12 inch, after that I was fine.</p>
<p>Some of the mac features are really helpful for managing your windows, you can use expose to press f8 and make all your windows become really small and easy to navigate or f9 to make only windows of the same application spread out and be easy to manage. Plus with Screens which will be on OS X Leopard, you'll be able to virutal screens, this means at top right corner of your screen will be a little icon, each time you press it you'll look at a new virtual screen, this helps tremendously with managing windows.</p>
<p>All in all, 12 inch or 13.3 inch will work very well and be perfect for a student on the go, I use mine for everything -- watching movies, tv shows, all that jazz and it's great. You will definitely get used to it after a day or two.</p>