Thanks for the link, I didn't know that project...
Actually what we use in the Arch workbench is IfcOpenShell http://www.ifcopenshell.org/
As far as I can see the main functionality of xbim is to provide IFC import and export, which is exactly what ifcopenshell does/will do (export is being implemented right now)
Looking at the code, xbim seems more mature than ifcopenshell, but it also looks pretty windows-only... There might also be license compatibility issues. So we're probably better
with ifcopenshell, not to mention the good and productive relationship we have with its author.
Anyway, it's thrilling to see all those IFC-based project appearing... This really shows that the opensource world has chosen its side in the pro IFC / against IFC debate...
Do we make use of these tools for our bim component? http://xbim.codeplex.com/