In web marketing, Ajax and DHTML are useful tools. However, to ensure proper visibility of your site to search engines, make sure you are using them appropriately and not actually blocking essential content.
Ajax allows you to build web applications. It allows a webpage to load new information without requiring a new page load. That delivers faster, smoother web interaction and generally makes visitors happy. DHTML is a method used to create things like drop-down menus, simple animations, and special effects. You don’t need to understand the technologies to understand the risk they pose in SEO.
Ajax loads content by using JavaScript. Search engines can’t read JavaScript, so any content you load using Ajax is effectively hidden from the search engine. If you have content you really want a search engine to find, don’t deliver it using Ajax.
Google does crawl Ajax-driven content but results are mixed, and it’s hard to say whether this will really help with rankings. Play it safe and avoid the use of Ajax for major content.
Ajax is a nifty way to build great web applications, including shopping carts and search tools. Just be sure that you don’t hide text content behind an Ajax application.
DHTML also loads content by using JavaScript. Same problem. You can make DHTML menus in such a way that a search engine can still find the links.
Ask your designer to make sure that he builds the menus to degrade gracefully. A webpage that degrades gracefully provides basic navigation and all content in a sensible way, even if the browser visiting it doesn’t support JavaScript or DHTML.
Take what your designers promise with a grain of salt, too. They’re totally focused on designing something great. You can verify whether your page’s DHTML navigation degrades gracefully. Open the page in Firefox. Using the Web Developer toolbar, disable CSS and JavaScript. If you can still see the links that are in the drop-down menus, your page is perfect. If you can’t, go ask the designer to redo them.