Sometimes these terms are pretty funny and alive when first coined, then die off and become cringeworthy. There are degrees of cringe, too, like the circles of Inferno. You know you're reaching the inner circles when articles start to appear like "How to Keep Your Code Ninja Happy: A Manager's Guide" :)

I wonder if it's an American thing or a programmer thing. Software development is still new and widely misunderstood, and most metaphors to existing disciplines suck. That's the real problem with "software engineer" (as it is with "software architect"). So people come up with wacky terms that are free of entrenched connotations and convey a playful creativity that's actually closer to what good programmers do. But they're disposable. Once the novelty is gone, so is the reason for using the term in the first place.

Edit: "hacker" is an interesting case. It's been around long enough to have had all the life sucked out of it and yet it lives. Perhaps that's because the term (as used here) shadows a more exoteric usage that's sinister and scares the corporate types away.

"Monkey," "Ninja," etc may be informal, (I don't know how you mean naive,) but it at least doesn't usually imply posturing.