There is a lot XML usage going on. I use it in an application for ADT 2007 I'm developing in Visual Studio 2005 and will export to Fi2xml. AutoCAD Palette Auto-hide Speed freeware modifies fixedProfile.aws (an xml file) that AutoCAD based applications uses.
The Mars Project from Adobe Labs with an XML-friendly implementation of PDF syntax with the new file format Mars (.MARS file extension).
Microsoft .NET 3.0 Framework includes DWF (.dwfx) Viewing Capability based on the XML Paper Specification (XPS) from Microsoft. But even the existing DWF format uses a lot of XML in it. AutoCAD's .CUI, AutoCAD Standards Check File (.CHX), Autodesk Project Information (.APJ) files used by ADT as many others are XML files.
XML Marker - A free XML Editor that uses a synchronized table-tree-and-text display to show you both the hierarchal and the tabular nature of your XML data.
XML Notepad 2007 - A free XML editor from Microsoft. Version 2.2 published 11/27/2006.
3D PrintScreen that can grab a 3D model from any OpenGL based application and save to 3D XML and the 3D XML Player are free from Dassault Systemes.