There is a current (& lively) discussion on Geni, started on 07/29/12 by Sharon Doubell (curator). She opened this discussion by asking the question “Does Pepin, the Grandfather of Pepin I, exsist?”
http://www.geni.com/discussions/110536
Sharon is attempting to clean up the profile on geni, and I thought that if there is a similar operation on WikiTree that there may be useful info to be had from this discussion.
(no, no, no, I am not at this time offering to dive into this tangle:))