If I was being honest and was going to do it again, and as much as I dislike this suggestion, I would purchase a Macbook pro with the higher education discount. It would have only come out slightly more expensive than my current and I feel would've lasted much longer. As it is, after 2 years with my Sony I'm looking for an excuse to buy a MBP.
They're smaller, lighter, VERY good battery life comparatively (my VAIO is 2 years old and dies after 5 minutes whereas my mates MBP still lasts hours after the same amount of time) and also easier to use - the touchpad is godly.
Then just bring your own extra screen/mouse and you're set - dual screen is ridiculously helpful for essays - your reading texts on one screen and the essay/draft on another.
Edit: Just to clarify I'd never consider bringing only a desktop. Portability is ridiculously helpful and computers are far from free 100% of the time - dissertation period anyone? Also when visiting places you can just chuck it in a bag and not worry about it. If I'm going to stay at my mates for a couple of days I'll chuck my lappy in just for when he's busy / we're just both chilling.
Oh, and I'm far from a fanboy, I just really believe that MBPs are better due to the touchpad, battery and portability.