BOO! Hehe. What is this caution crap, anyway? Well, before you get all CSS-happy, you have to understand the limitations of CSS [imposed by browsers]
First, not all browsers support it. Which ones do? Well, here's a list as of August 1999:

• IE 3.0 and up
• NS 4.0 and up
• Opera 3.5
• Emacs-w3

This means that if you build your site using one stylesheet for everything, discarding good ole HTML, chances are there will be many people who won't see your site in all its intended glory. Don't depend on StyleSheets on your site :) Use them to enhance it, but don't make them a requirement.

Well, and, of course, the bugs:

• Netscape Navigator 4.x incorrectly ignores any style sheets declared with MEDIA values other than screen.
• Microsoft Internet Explorer 3 for Windows 95/NT4 does not support BODY background images or colors from linked style sheets.