I've updated the Special:Export schema in MediaWiki 1.5 to include a <siteinfo> chunk with some site configuration information.
For example at: http://commons.wikimedia.org/wiki/Special:Export/Chlamyphorus_truncatus you can see the custom namespace assignments.
and at: http://es.wiktionary.org/wiki/Especial:Export/aristocratizar you can see that wiki's marked as case-sensitive.
This should make it easier to ensure that page titles are processed correctly on import.
I've also added an xml:space="preserve" hint to the <text> elements, which may or may not keep some overzealous tools from stripping the whitespace automatically.
The XML Schema definition for version 0.3 of the export format is at http://www.mediawiki.org/xml/export-0.3.xsd and in the docs/ subdirectory in MediaWiki CVS HEAD.
We'll be providing the full-wiki public data dumps in this format starting in a few days, replacing the old SQL dumps. For the reasons behind this switch, see my earlier posting:
http://mail.wikipedia.org/pipermail/wikitech-l/2005-May/029298.html
-- brion vibber (brion @ pobox.com)