This is the .NET code used by the Revit 2012-2014 families of products that support IFC export. The open source version can override the version that comes standard with shipped Revit. Revit 2013 and 2014 contain both IFC export and IFC export UI overrides, which contains options not available in the regular UI, such as ifcXML and ifcZIP support. The Revit 2014 version also works for Revit LT 2014.
Brilliant to get frequent updates between releases for IFC exports, and great possibility to intereact directly with the developers through the discussion forum. Still, there's a bit of a way to go before things work reliably... Also wish for a better UI to get control over what comes out.