These days, it's a little bit of a turnoff. At a minimum a job ad including "ninja" or "rock star" communicates to me that you can't otherwise quantify what you want, so you use a vague description that doesn't help a prospective candidate judge whether she's suited for your company.
I'd rather see a job ad that's much more explicit in what the company wants, whether that's technically ("5 years of Python"), attitude ("We want someone so passionate about chocolate websites that she'll jump up and down on the conference room table... but please, don't, it cost us a lot of money for that table"), or in visibility ("We expect to recognize your name; this is a job for someone who probably needs no introduction").
It sort of reminds me of the "Everybody is a winner" method of child rearing. There is quite a wake-up call when you realize that everyone is a "ninja".
"We're Looking for a Ninja BrainFuck Programmer. Come hang out sometime and we'll see if you're a fit."
That's it. Anything else -- resume, phone screen, FizzBuzz, whatever -- and it's obvious they're pretending to be cooler than they really are.
And companies have to be pretty professional to tolerate some of their staff being from different cultures (narrowly defined) ... and one making such a advertisement sure doesn't sound professional to me.
The gist of my post was:
Originally, it was a way to suggest to a technical candidate, "Don't be scared, our place of work respects technical people." It was a code in a way for, "We're not a boring bank. Or if were are, you still might have fun here."
Now I think the term leveraged in the opposite interest: "We need YOU, the candidate, to be awesome. But our wacky language still gives no clue about us, the employer."