Use the Source, Luke
There are some really wonderful web development tools out there. They range from simple WYSIWYG editors to complete multi-site management applications. It is quite easy to build and deploy rich, full featured, incredibly sophisticated web sites. This is, for the most part, a good thing. There is a down side to using tools like FrontPage or NetObjects Fusion or Dreamweaver, however. It's not a problem with the tools themselves, specifically. The problem is a lack of knowledge of HTML by many who use them to develop web sites.
Everyone who does any work building web sites should have a fairly good understanding of the HTML specifications and of Cascading Style Sheets (CSS). Now, it's been pointed out to me that with todays web development tools you don't need to know anything about HTML or CSS to build quality web pages. Point, click, drag, drop, publish, it's Miller Time. It is true that you don't need to know HTML or CSS, but I maintain that even if you never hand code a web page in your life you still need to understand the basic, fundamental foundation of HTML in order to get the best out of the medium you are working in.
When I started working on the web back in late '94, early '95 most of the web development tools were just text editors with a little functionality, like prefabricated tag generators, added on. Most people used vi or notepad to write HTML. Now I'm not saying that everyone should go back to using text editors. It would be impossible to do so and be able to keep up with any fairly large site like the Army Home Page http://www.army.mil or Army Knowledge Online http://www.us.army.mil. It is, however, very helpful to know what to look for, and where to look, when something just doesn't look right ("Why is that table not aligned correctly?") or when visitors to your site have problems ("The menu on your site doesn't work!") yet it all looks fine and works well for you. Understanding how the code works will allow you to make better use of the WYSIWYG tools, too.
There is another issue where being able to understand the source for a web page will come in very handy. Most of the WYSIWYG development tools have a tendency to generate source that is not optimized and many add lots of extra text that can bloat the size of your pages. This isn't something most people who are writing the pages notice. Generally, the web developer has a LAN connection to the web server so pages just pop right up. However, most of the time your site will be visited by people connected to the Internet via 56k dial-up. Or slower! Extra text and, even extra white space, can slow a page down enough so that users will just hit the stop button. Everyone knows about keeping the graphics small to help speed up downloads but how many know about the performance issues that occur because of the way HTML is rendered?
Understanding the source is, as Obi-Wan might have said, the key to understanding the web.
[Joe Klemmer has been working in the computer field for 18 years, 10 of those online. He can be reached at firstname.lastname@example.org]