I am a college student and I am in the same boat as you and am stuck deciding between the Air and the Pro. However, I am leaning towards the Pro because of the upgradeability because college gets expensive with tuition, housing and other "extracurricular activities" 😀 and honestly the only advantage the Air has over the Pro is the wow factor. It is not worth dishing out the extra 600 bucks. When you are up at 2 AM trying to write a paper in the library, do you really care what others think about your laptop? Or would you rather have the 7 hour battery life? Portability is not going to matter that much. 4.5 over 3 pounds is well made up by the battery and most likely you won't even notice. Plus, as I mentioned before, you can always upgrade the Pro and so it should last you at least 4+ years. Right now, the Air will work for you, but remember SL requires at least 1 GB of RAM. Tiger required 256 MB and Leopard required 512MB. So, in like 2 years when Apple releases a new OS (which follows their usual cycle, i am not pulling this out of the air), the requirement will be more than 1GB of RAM and then the Air would seem sluggish if you tried to do anything intensive. With an upgraded Pro, there would be no problem! Plus in like 4 years, the lines between the Air and the Pro are going to be really blurred and then you can buy a laptop that is also light and future-proof.
I don't know if I have convinced you or not, but I have just convinced myself 😀 to go with the Pro.
If still stuck, you shouldmake a pros and cons list because no matter what everybody says, you will rank features (RAM, weight, etc.) differently than others! Good luck deciding!