I just wanted to add in a quote from my old book called "Build Your Own Website", by Robert L. Perry. It teaches you the basics of HTML, and the concept of how to write HTML properly. However, as each day passes, it is becoming more and more out-of-date, seeing that CSS and XML are replacing HTML tags and attributes. Sounds like a load of jargon? I'll keep it at that, then.
"Brian J. Dolbeare, who designs web pages for a major corporation, solved - in five minutes - a nagging problem that experts from a leading Internet company overlooked for almost a month."
Of course, it is most likely this problem was caused by a rubbish What You See Is What You Get (WYSIWYG) editor like FrontPage or Dreamweaver. That's when knowing the HTML does help a lot, and if you know it, you have control over everything on the net.