Also there are a couple of cases where the converter will only be able to do G1 continuity instead of G2.

That will happen in some cases at the boundaries of open meshes and also at vertices of greater than valence = 8 (more than 8 edges coming off of a single vertex).

But these are not good things to have for sub-d meshes anyway so I don't think they are likely to run into very often.

- Michael