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").
I don't like to see such colloquialisms in job postings, but as someone who has done a fair amount of hiring in my career, I also don't want to see them on resumes or CVs unless you've worked for Rockstar Games, real Rockstars or Ninjas or on a game called Ninja.
IMO, those terms are grossly outdated and are/were often representative of companies that are a little too full of themselves.
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".
While I agree with many of the detailed points made by others in this discussion, I can put it very simply: it makes me feel like I'm not a member of the culture of the company.
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.
"We want rock stars" seems is used by some companies to mean "We want someone who is 5 times more productive than average but who will work for much much less than 5 times average pay."
I hate it and always try to avoid job postings that contain those terms. It's usually deployed by inexperienced/naive/arrogant teams and/or companies trying to sound "hip" and "with it". There's no way to measure what "rockstar" or "ninja" means ... for the most part, in my experience, I've found it most often to mean "superhuman", i.e., someone unrealistically and absurdly better than everyone else, who can meet 72-hour deadlines for a whole project (real encounter I had). It's definitely a bad omen when someone uses those words and an instant, severe reduction in respect for the company/interviewer.
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."
I don't like it, because it goes again my own beliefs in what constitutes effective teams. As a geek herder, I can't think of anything worse than a team full of "rock stars". The best teams have a mix of good people who excel at different things. For example you never see a job ad for "compulsive documenter" but every team needs one.
When you take a job, it's an investment. You want to make sure that the company you are investing in takes itself very seriously. Asking for Ninjas and Rockstars to fulfill an important role? Works only if you're casting for a movie.
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").