I'm in the middle of building this:
When I realized that I tested it for IE and NN6 but didn't try it in Opera 5. I got a shock when I saw that it messed up pretty well in that browser.
Ok, so I haven't validated the pages yet. But this is the first site I've built that came apart this way in Opera 5. And what's irritating me most is that I don't really know why it looks so bad in this browser.