Personally, I am a bit skeptical. For the most part, JavaScript (especially DHTML) is not used like Perl where there can be a general way of doing something. While its true that there are tons of JavaScript libraries on the web, code from these repositories usually has to be heavily modified before it is usuable in a situation that is applicable to the designer. DHTML is even less library-oriented, as it is integrated into part of the design. Additionaly, DHTML tends to be verbose (hell, just look at some of the DOM calls, you can see where the Java in JavaScript comes from) and is therefore is stored in a separate file as to allow it to be stored by the browser. Creating huge amounts of DHTML on the fly (and HTML::Widgets::SelectLayers certainly does create a HUGE amount of DHTML) would not be good for pageloads (laugh all you want, but 10k is still a 2 second download on a dialup).

Thats not to say there wouldn't be uses for this module. It could be useful to create a multi-page presentation that had to be enclosed in 1 file, or perhaps even used to generate code that could be used as a starting point for a more complicated design. Definately worth giving it a look if you need something like that...