Who Owns Your Digital Files?

If  a client asks for your digital files (on work you've done for them, of course) do you have to give them the files? That question comes up again and again. I saw that issue being discussed at designerstalk awhile back. There were a few posts describing a few somewhat devious ways to hand over the files that would render them difficult to use by the client (who is taking the work in-house). But the right answer, as posted by a few participants is basically the short version of what I've written in this FAQ: Do I Have to Give a Client My Original Digital Files?