I'd also just like to set something straight about modafinil. A lot of people have the idea that it's this amazing drug that means you can study/work/play video games/party all night without sleeping and feel fine in the morning. Not so!
Whilst you may be able to stay alert without having slept all night, you'll still feel lousy the following day.
Also, I've never experienced and increase in my base line concentration level. As in, if I take them I'm not suddenly much more able to concentrate on my work, or suddenly a genius or anything like that. However, if I'm really tired, they do enable me to concentrate normally, alleviating that "wooly head" feeling.
(Before anyone shouts at me, I'm on modafinil for medical reasons, to treat idiopathic excessive daytime sleepiness, I'm not using them recreationally. Although, of course, I have experimented with the staying up all night thing, out of curiousity)