This reminds me of another post Yudkowsky made on a very similar topic.

I would consider most of the people here to be informally operating on at least a milder version of Crocker's rules.

I can think of a scenario where the colour red tends to have the opposite effect... http://en.wikipedia.org/wiki/Redshirt_(character)

The sensitivity to irregular caffeine users is just due to lack of tolerance. It can still be avoided by just reducing the dosage compared to regular caffeine users.

Sure, I can imagine caffeine impeding long-term learning from exam revision.

But I find the increased focus to be much more important, for an exam that I've already studied for, and for material I will very likely never need to know in quite as much detail ever again.

There's 2 different kinds of studying I do. Studying conceptually for the long term, and cram time for a specific exam fitting in all the fine details, and then quickly regurgitating them. If it takes exam revision to significantly enhance the former, then I already learned too little, too late. That said, I commonly use caffeine for the latter with no regret of the side effects.