It's something you have to pay a huge chunk of money for. And it doesn't mean you're any better, or have a better reputation in your field, than somebody who hasn't forked out to get there.
I relate a great deal to NC's description of herself. I'm not the cleverest solicitor, academically, that you'll ever meet. What I am though, is very good at practising my area of law, and teaching others how to do it as well. I'm very proud of the work I do with my mentees!
I wish I practised employment law though (in another life that would've been my niche), as I'd have had a chance to work with NC then. I think it would be a brilliant experience.