Monitor says it all, mate. I'm getting a 22" HDTV to use as one in college. Plus, if you sit on the internet for hours like I do, it'll be right nicer to look straight ahead at the screen like you would with a desktop setup as opposed to down at the screen, even if it is sitting on a desk.
I also think actually trying out the machine is very important. I went to the store today thinking I would be getting a 13" MBA, but I absolutely changed my mind. The 11" is much more for me due to its proportions and screen shape.
When you're in college, you take your laptop everywhere, and IMO, the MBA is perfect for that. I know a friend of mine who's in college and has a 17" laptop, and I can't at all imagine lugging that thing with you in a backpack all day long, in addition to your books. Even today at the store, I chilled on an MBA for a bit, and then picked up the 13" MBP that was sitting beside it. My first thought was "Oh my God, this is heavy as ****." I think the portability of the Air makes it the perfect laptop for college kids.