The DWFx format has been added to AutoCAD 2009. DWFx is based on the XML Paper Specification (XPS) format from Microsoft. You can view and print DWFx files using Internet Explorer 7 on Windows Vista and Windows XP (with latest updates for .NET).
In AutoCAD 2009 You can plot or publish to DWFx, attach DWFx files as Underlays, and read DWFx files using Markup Set Manager. You can still and will continue to be able to plot the older DWF format as well.
The soon to be released FREE Autodesk DWG TrueView 2009 will provide the ability to open and view DWG or convert to DWF or DWFx as well as much more including the much requested measuring/inquiry capability. See the Beyond the Paper posting DWG TrueView 2009 is cool.
The soon to be released and FREE Autodesk Design Review 2009 supports viewing, some editing, and markup for both the DWF and DWFx formats.
The free web service for viewing your 2D and 3D files from any operating system through a browser Project Freewheel (http://freewheel.labs.autodesk.com) now supports DWFx and the official Autodesk Freewheel (http://freewheel.autodesk.com/) perhaps in the future.