Physics/Statistics major here.
Most of the time I just use Safari, Mail, iTunes, etc. for browsing, email, and music.
When it comes to assignments, I sometimes have to use Windows. I would hate to dual-boot and actually have to use Windows for anything more than the ONE statistical program I need, so I use VMWare Fusion. I get my work done in XP, use OS X's screen capture capabilities to grab my graphs without even needing to export them, and go right back to OS X. Then I use Pages for any reports or essays I have to write up. I like it a lot better than Word, and makes me so much more productive.
As for needing Windows: for anything in the sciences or in engineering, there's a large chance you'll eventually run into a class you need Windows for, if only for a single program. However, I would NOT recommend ever getting a Windows computers just because of this. Even though I'm forced to use it once in a while, 99% of my computing time is still in OS X, and it's well worth it if you can afford it.
And finally, when it comes to recreation, I play Unreal Tourney 2004, which the MacBook handles beautifully on medium/high settings. I'm hoping it will fair as well when UT 3 comes out. The Halo demo also played well, but sadly it's no longer available.
Also, to other college students (since the OP already seems to have come to a decision on this matter): I would NOT get an EeePC as a sole machine for college. It's a great device that would be wonderful for notetaking/email/web use, but for much more, it would be quite difficult to use for college. I've tried out one of them, and it has a really amazing form factor--you can probably fit one in your pocket if you have big enough pants--but the small keyboard/screen size are really very difficult to use for any kind of long-term use like working on a project or writing up an essay. It'd be a great second machine, though.
