There are various things that Jim Butcher has said over the years. Most of them made it into the game in one way or another, but you don't always see all the reasoning behind it.
Well someone has taken the time to collect every scrap of information that Jim has posted (or said - some the links are to youtube videos of him at cons) on the Dresdenverse. You can find it at:
http://www.jimbutcheronline.com/bb/index.php/topic,21772.0.htmlRichard