DHTML is a combination of Javascript, CSS and HTML. It's fun to do and provides interesting effects on web pages. However, there are several downsides to making DHTML the basis of your web site.
First, if one of your goals is to have your site indexed by the search engines, DHTML might cause problems. That is because your content is created on the fly. Therefore the spiders and bots that crawl your page will not be able to read the content.
Second, what might look good on your browser, might not work as well or at all on other browsers.
Third, since more and more browsing is done with PDA's and cell phones, you might be losing visitors. Generally, these devices can not understand dynamic content.
Fourth, since there is growing concern about viruses, worms, and other nasty stuff, many browsers have installed programs to block active content. Usually, the visitor can over ride this, but do they really want to?
Finally, most people are gearing up with anti virus programs, pop up blockers, and other security programs that will make your magical scripts fail to work.