Okay, as one of the original posters to this thread and its predecessor, I have to side with bdsmbill. I'm against using celebrities as characters under their own name, but have no objection on moral grounds to either using a celebrity and changing their name (by which I mean changing it to something unassociated with the real person, not just using the name of a character that an actor played or reversing their first and last names), or to using a celebrity as a physical template and admitting that you've done so.

On the other hand, the risk of describing a character as looking like Nikki Cox, Avril Levigne or Beyonce is that I, for one, have no idea what any of those people look like, so you've told me nothing. I think you have to actually describe them, in addition to using the 'celebrity equivalence'. That way, people who DO know what Nikki Cox looks like can have an exact picture in their minds, while shlubs like me can make make do with "long, black hair and high, small breasts' and our imagination.