What's wrong with personality tests?

The Myers/Briggs personality test is suddenly popular again on FaceBook and it made me think about what bothers me about those sorts of test.

• I hate dividing people up into categories. At least Myers Briggs gives you 16 and not just the either/or of extrovert/introvert. But still.
• It's easy to write a single personality description that nearly everyone will see as applying to them, especially if it's nice and general. I think this is because we mostly remember the bits that apply and ignore those that don't.  Tests that do this are meaningless.
• The worst personality tests divide the world up into bits and then force you into a mould - everyone fits into one or the other personality type by definition. This tells you more about the author of the test than about you.
• The best personality tests ask you questions, then take your answers and feed them back to you in paraphrased format. So you're getting back what you put in and it feels eerily accurate but it's not actually telling you anything you didn't know. Except that the author's underlying beliefs about how to divide up the world usually end up shining through anyway.

But I have to admit that personality tests can be fun. I think I prefer the ones with colours, or elves, or "which Sherlock villain are you?" because at least they don't take themselves seriously.