why are you all buying $2k macbook pros to browse youtube/facebook and look through uni lecture slides? this would be doing exactly what you said you hope to avoid in buying unnecessary hardware.
if you're using it at uni, a hybrid might be a good choice - have a look at microsoft surface (the pro which runs full windows 8 comes out in January), HP envy or even the dell variations aren't too bad. you can have them in tablet form for browsing casually and in laptop mode for writing essays and what not.
Just remember that Uni requires a lot of walking both on the way to and at campus, and power points (the thing with electricity not the slides which you will rarely get in this format) are not everywhere you'll be. Lightness is key here.
I'd go MacBook Air or some kind of ultra book. You aren't going to be doing gaming or hardcore video editing unless you're in those specific courses.
Hybrid would be my choice. I getting a Surface Pro when it does come out. 5 Hours is decent enough hopefully there will be powerpoints at the places I'm at. Surface RT is also a good choice with Office RT which is excellent version of Office which has Word/PP/Excel/Onenote (obviously minus some functions) but it'll last you at least 9 hours!