The Pixologic documentation team is happy to say that a general document explaining normal maps in some depth, and how they relate to bump and displacement maps, is now available at http://www.zbrush.info/site/index.php/Bump%2C_Displacement%2C_and_Normal_Maps . This file is fully editable to registered zbrush.info users.
This is a section of the full ZMapper documentation, which will be converted and posted to zbrush.info over the next short while.
Happy ZBrushing!,
Ken
Thanks for your contribution, I start this day a lot more informed…Well done.
Many thanks, that is really useful. Your explanations are clear and very illuminating, especially for someone who has had a hard time understanding all that. Much appreciated. 
Thanks Ken!
This is completely editable so I encourage everyone to get in and add what they can even though I know Ken has done a fantastic job of researching and explaining normal maps! 
Ryan
I’m glad people are finding it useful. Hopefully there won’t be too much editing needed. Once the main body of ZMapper documentation is up, that might be a more interesting thing to edit, as I’m sure many users will want to share tips and techniques.
Cheers,
Ken