Geoff Zeiss shared via a post at the Autodesk blog: Between the Poles that Autodesk is now making the IFC Exporter for Revit available as open source code.
Access to the code can be found at the SourceForge Repository. For more information about IFC you can visit the BuildingSMART site.
Emile also posted about this at the BIM APPS blog. According to Geoff's post:
The Revit IFC Exporter Open Source Committee is chaired by Emile Kfouri, BIM application development manager, Architecture, Engineering and Construction Solutions, Autodesk.