I recently received an email from someone at NIST, asking me to look into register for and post on an IFC-BIM Exchange Support Forum. I haven't done either of those things yet - I'll get around to it because I do think that it is important for users with experience with IFCs to talk about them.
But I do have to say that I am a little sick of hearing about IFCs, especially from vendors. We had to use them on a project, and they were really frustrating. The result is that we have very dumb objects in our model. The geometry was preserved, but we have no actual geometric properties (no width, no height, nothing!). We also cannot snap to these objects in Revit, which obviously slowed down our modeling process.
Vendors need to stop saying that IFCs work. They don't. Ask anyone who has used them. The most aggravating part is that they could work if vendors would dedicate to them.
I am clearly not against using something that "isn't quite there" (look at Revit!), but calling IFCs 'experimental' seems generous at this point.