XML Developers' Conference http://www.gca.org/conf/xmldev99/
Take a look at the membership list: http://www.w3.org/Consortium/Member/List
Document presentation can be tailored to specific contexts, media and users. Documents and parts of documents can be reused and repurposed. Information can be drawn from a variety of sources without those sources needing to know final presentation. Structure can be constrained and documents validated to such constraints. Parts of documents can more easily be integrated with database systems.
CSS is really only usable with XML if the presentation and structure have the same ordering which is rarely the case with large documents that you are trying to present in different contexts.
XSL is now reaching a stability that makes it well worth pursuing. Note that the transformation side of things is more mature than the formatting side. For online, XML->HTML transformation via XSLT works very well. Eventually XSL will provide excellent transformation to print too.
I'd avoid a generic programming solution like Perl for document presentation. XSL is designed specically for the purpose and any initial learning curve is more than made up for by the benefits of this. -- James Tauber / email@example.com / www.jtauber.com
Approaches to developing applications: http://www.naggum.no/worse-is-better.html