How can you gamify the recruitment of new employees? We recently had a user on our site ask if they could add game mechanics to their employee recruitment. To be honest, I'm having a little trouble finding solutions for this. I'd really appreciate any insight you guys might have.

I guess my first question is, who would you incentivize for this, and how? Are there any case studies that cover a scenario like this?
I would try to work on stimulating rejected candidates to become referrals. 

Every candidate who has been rejected is already quite well into what the job is all about. S/he should be very good at explaining the job requirements. (The pitfall of the majority of job ads, IMHO is that they bitterly fail at explaining what the job is about.) 

At the same time rejected candidates must be likely to know colleagues good for that job. And it is in their self-interest to promote those colleagues, because they would have less competition for all the other vacancies.