I'm in college and actually sold my 15" MBP and purchased an 11" MacBook Air in the middle of the year. With the books, binders, and additional research that I needed to carry around to the library, the MacBook Pro was extra weight I wasn't willing to carry... especially coming home late from the library at midnight or one. If you're simply planning on working in your dorm, stick with the 15". Otherwise, I value the portability. I have written many smaller 4-5 page papers on my Air. If I'm going to write a more substantial paper, I generally use a machine at the college since the 11" screen (and I believe a 13" screen too) feel cramped. I am 100% satisfied with my decision. Hilariously enough, after purchasing my MacBook Air 11", my roomie loved the portability and speed of my machine that he sold his Pro for an Air so we both have 11" Airs now and love them. The largest constraint the Air faces, aside from the GPU (which doesn't matter to me), is the SSD size. If you have a lot of music and/or photos, it may be difficult to fit everything onto the SSD. I definitely had to scale down a bit. Still, I haven't run into too many issues. I am planning on investing in a new external HD soon though and partition it as a back-up and a regular ol' external.
Additionally, a huge recommendation I have is to download a free application called Bumptop. Bumptop, though not distributed anymore can still be found around online, was purchased by Google supposedly for Android. Bumptop gives individuals extra screen real-estate on their desktop. It's like a 3D desktop. Downloading Bumptop when moving to the 11" screen definitely made the screen not feel cramped. Also, though going from a 15" to an 11" screen may feel like a tremendous change now, it seriously becomes normal. Amazingly enough, people do indeed get used to their surroundings and living within their constraints.