Firstly i would not recommend anyone taking unprescribed drugs.
But with the above proviso i can say. It does work but don't expect to be awake for days. It can extend your wakefulness but more importantly it allows you to concentrate better during that time. As a study aid it can be very useful.
To say it has no side effects is a little spurious. It can have a lot. It can give a dodgy gut so never took it for long periods. As will all drugs there is also the risk that you may be alergic to it. The other up side is that it also acts as a very mild mood enhancer so your awake, alert and in the mood to work.
4 or 5 days seems like asking for trouble but getting you through a day after a night of very little sleep can be very effective.
The fact that the armed forces use it, isn't really a recommendation. Before this they used Amphetamines and we all know the risks there.
The big benefit of Modafinil is that it has none of the edgyness of stimulants like caffine.
Is it a miracle drug? The bigger issue i think is what if for example i took it all through exams and got good grades.The guy next to me only managed a couple of hours a night concentrated study and didn't do so well. Was he disadvantaged? did i cheat or just use the resource available to me?
Universities will tell you its use is minimal. I'll tell you its not. So is the playing field level?
The other interesting thing is that since its introduction and use recreationally the incident of people claiming to be narcoleptic in the US has gone up something like 800%.