I did the advanced driving course with the IAM a couple of years ago. Did a few drives with the observer, and passed the test with the examiner (in my mk2!).
It was very much as I expected, although they did encourage slower speeds than I envisaged. Some of what they taught I didnt like, in particular the wheel suffling, but overall it was worthwhile. The best thing was having someone experienced evaluate your driving habbits and provide constructive feedabck so you can improve the safety of what you do.
I have since become more aware of hazards, and more cautious at times as a result. But being human, I have also had a couple of inctances of poor judgement too putting myself at risk, but thats down to me as an individual.
Most of us are confident behind the wheel, and are happy in how we go about driving a vehicle, its well worth having someone hold up a mirror and iron out any 'faults'. As a result of the course I can however be more nervous passenger!
The books/literature will go a long way to introducing you to anything your not already aware of, but a couple of drives with an observer would be worth it I think.
Gives you a slightly better chance when the roads get hairy!