Facebook forbids a lot of things, but that doesn't mean that they don't happen anyway. Before you ask me, I don't have any data about how many multiple accounts there are on FB, but my anecdotal experience suggests that there are many. I also think that it would be very interesting to actually take a survey about that, and about how many people would like to have multiple identities without violating the TOS.

About resharing, of course if you use the same real name in both services that would't be different from circles - it would just make it much harder to reshare, but by no way impossible. That's not my wife's use case. But if you use different names, tracing you becomes pretty difficult.