I've used numerous laptops in my days (which are not long), but I've been through college with one and I have some wisdom for you.
Order of importance when buying a school laptop.
1: Build Quality
Don't kid yourself. You'll probably be living with some guys who will throw things, run into things, and break things. I had roommates like this, and even though they were great guys and are still great friends, they broke crap. Maybe you're roommates won't be as bad, but consider this. You will be moving this computer around a lot. Taking it to class, moving it from your desk to the couch in your dorm, taking it to the library, taking it to another dorm room, etc. It will get used and possibly abused, so make sure it's built well and not made out of cheap plastic. Larger laptops are more prone to suffer from flex and bending, so do yourself a favor and research your laptop before you buy it, otherwise it's not going to last you for four years.
2: Keyboard
This should be a no brainer, but it's not. You are going to be writing A LOT in college. You will be typing out more papers than you can imagine, and if you're going to be doing the note taking thing your keyboard will really get used. Make sure your keyboard isn't crappy. It needs to be sturdy with no bending or flexing and the keys need to be strong and have good feedback. You don't want to have a cruddy keyboard that gets sticky and a couple of keys stop working. That happened to me and there is nothing worse. My left shift key failed, so I had to learn how to shift with my right hand which sucked. Also, some keyboard layouts are strange so make sure you get one that feels natural to you.
3: Battery
Yup, its really annoying going to class and running out of batteries in the middle of a lecture. That happened to me a lot and it sucks. I'm not just talking about one class here! Usually you will have three or four classes in a day with little time to recharge in between. Get something that can give you three hours of battery life. If that's not possible then get a second battery. You will not regret it.
4: Display
You will be spending a lot of time on your laptop in college. If you get something with too little resolution you will get tired of switching between windows every two seconds. If you get something with too high resolution then you will get a sore neck and eyes from straining and leaning forward to read the screen. I currently have a 1920x1200 display on my 15.4" Dell. I love the display, but I can't spend more than an hour or two at the computer before I start feeling it in my neck and back. Be smart about this one! You shouldn't get more than 1650x1080 on a 15.4" in my opinion. If I were buying this laptop again I would probably go with the 1440x900 screen. Also, really think about LED backlighting. It will give you longer battery life and it will allow you to use your laptop outside. Standard backlight displays are useless outside, especially with the super glossy screens you see nowadays.
5: Service
You might think that you're a computer genius and that you can fix everything on your own. I made this mistake and only got the one year warranty with my college laptop. Here's the problem. Laptops are not like desktops and you can't just replace a part when something stops working. There are a lot of integrated components, and things just crammed in way too close. Things overheat, wear out, and break down a lot faster in a laptop than they do in a desktop. Do yourself a favor and cover your back for at least two or three years.
I'll add more if I think of it