I think there are quite a few that are "trying it out". I know that in theory, it seems like there is a lot of benefit to the back-and-forth ability of IDX versus the one-way nature of IDF and DXF. At my previous job, we were trying it out and implemented a standard of always accepting any changes. This made the feedback loop that is part of IDX a little easier (granted, we didn't have very many instances where something would want to be rejected anyways). We ended up using it just like IDF really, and the benefit is that you can bring the design over to CREO and then do some things with the model (place in top-down-designs, make measurements, etc.) and then when there is an update, you can just use IDX to update what you already have and can save time of redoing any of that work. We normally started designs in ECAD and then just transferred to MCAD. There was not too much information coming from MCAD back to ECAD.
To me, the biggest gap that would cause the biggest problems was to make sure that when you wanted to do a sync, both ECAD and MCAD had to sort of pause what they were doing and sync. So, ECAD would create an incremental file and then you have to basically stop work on ECAD until you get a response file back from MCAD. If the MCAD response had change as well (not just accept/reject), then the MCAD would have to pause until they also got a response. So, it would make sense to almost "schedule" when you were going to do your incremental updates.
I think a lot has to be done in all tools to help show the status of changes, who has accepted, who hasn't accepted, etc. It might be the next-gen of IDX before that really takes place.
