To be honest, I've not revised a single thing so far and, apart from french, I'm breezing through the papers with A*'s. Don't follow my example though, I'm an exception to the rule, and I really need to revise for the coming exams.
Just to toot my own horn, I'm currently at an A* in english, all three sciences, maths, RE and IT. My statistics module is finished, that's an extra A* GCSE, I've just sent in my engineering coursework which should be a double award (A/A*), the French coursework was A*, and I've just finished my speaking exam with an A (it's the french exams I suck at most, and am not looking forward to).
Sounds familiar: http://forums.overclockers.co.uk/showpost.php?p=16495433&postcount=1?

Past papers are all good and well, but they shouldn't be used as the main resource for revision. If an exam has been written properly it should be testing your understanding in a subject and not your ability to rote learn. You sometimes get those belters that no one has ever seen before.
I remember once a proof for something came up and it was worth 14% of the paper, heard some very creative cusses from people after the exam

Anyways best of luck with your GCSE's, it gets much harder from there.