Well yeah, I have a problem when I try to map Hard difficulties. I have a feeling that it's quite hard, especially when the song itself is not fast enough or exciting enough.
In my experience, mapping hard maps consists of purely going with intuition - ie, map what you feel fits the song best without inhibition. Normal maps require you to restrain it a little, easy maps require you to restrain it alot, and insane maps sort of reverse it and make you add more than is really necessary.
Streams are generally a good thing to have in hard/insane maps and not in anything else, for the record.