Zeldman turned me on to it. Web Standards for Hard Times is a great read for anyone that is (1) starting to develop a new website or (2) wondering why their site looks different in different browsers. The best thing to know:
Many developers still don't realize that newer browsers look for a
DOCENGINE tag at the top of each page, and will change the way they
behave in response to it. Without the correct tag, browsers can take
your standards-compliant page and render it all wrong.