Since I am a Mac user, I say go for a Mac. They have the new airbook out, so that is pretty light for your commuting needs. They also have a bunch of other models to choose from (as you might already know from your research). I would get it from your campus computer store, or from the Apple store, because with you can get a 10 or 15% student discount on the laptop, and they have this back to school special (which they have every year) where they throw in a free iPod.

I never had any compatibility problems, except this one time when I had to make probability trees on Excel for my statistics class. For some reason the probability trees wouldn't show up or work.