The thing I find most interesting about Modafinil is how consistent the stories are about how people feel (and work) when they take it. Everyone talks of extreme focus, but perhaps a loss of judgement about what tasks are actually important. I don't have any particular conclusions about that - I just find it really interesting.
I've heard a fair number of people report getting no effect, and recall reading somewhere that there's a gene which separates modafinil responders from non-responders. It's just that non-responders tend not to talk about it, since it's much less interesting in that case.