If you want to know how the web works, why it often doesn’t, and what causes software to make you insane:
1. Read this very important post from Joel Spolsky: Martian Headsets.
2. Buy the most important book ever written on web design (which is actually for web people and regular people): Designing with Web Standards by Jeffrey Zeldman
These are sort of technical, but quite readable and fun. If you are in any form of web-related business, you need to read them.
(Thanks for the link, Guy.)