Separation of content (XML files in an XML database) from templates (XSL-T files in an XML database) from presentation styles (CSS, JavaScript & DHTML) is one of the most powerful and useful things a content management and application server combination can do - see also Content management system recommendations? and XSLT vs Templating?.

However from a Perl programmers perspective, you don't need to use an external standalone XSL-T engine such as Saxon, or Xalan (good though they both are). You can get your own application to do it it's self, directly or via a library, this is how Cocoon and AxKit and many other commercial systems do.

From the perspective of a Perl user you can use Matts excellent AxKit framework, or his XML::LibXSLT module directly from within your Perl code. I use XML::LibXML to manipulate XML files, template them with XSL-T, and save the output as HTML files! See Mega XSLT Batch job - best approach?, (in answer to Tilly's question, in testing on a 1Ghz Linux box, from one 1Mb XML file I was able to create over 2000 HTML pages, and associated folders in under 30 seconds!)

If used right XML is a very good tool, just remember it's not right for everything, no matter what some people say!

Another humble 2p