This article (from December last yer) is well worth reading if you haven't seen it already:

http://youngpup.net/?request=/articles/labels.xml

It demonstrates how DHTML can (and in my opinion should) be used to enhance the functionality of a page while still leaving the page completely usable to non-javascript user agents. It also require no additional HTML markup (other than the inclusion of the script). Obviously it isn't possible to be this well behaved with all DHTML applications, but it's a great target to aim at when working with javascript