I vote for "no POV-switching within a scene." It'll make me click the back button, seriously.

Multiple POVs in a fic are fine, though, when demarked by a new scene. I think of it as another issue than the one above.

I think multiple POVs are an old-fashioned thing - I'm reading an E.M. Forster story where he does it constantly, even within a paragraph. Can't say I like it much, but he's dead, so I can't make him toe the line, either.