Technically it is never ok to just hand over an authorship. We all know authorships are precious. But of course it happens all the time as part of scientific back scratching.
Both your examples are great. It is great publicity to get a movie director/actor (or whatever she says she is) on the author list. We would have never heard of that paper otherwise. I would put Lee Stapleton on all papers if it meant free publicity.
Nobel prize winner Andre Geim included his hamster as a coauthor on a paper: http://dx.doi.org/10.1016/S0921-4526(00)00753-5
(the hamster, papers = 1, citations = 12). My H-index = 11. Why do I bother?