I put together something called "wantmyjob" that used the OKCupid solution with making and answering questions about your workplace. But that really won't work for startups since they don't have a bunch of existing employees to recommend them. I'd also probably have to commit the cardinal sin of trying to charge the job seeker -- not so good.

Similarly, there are a lot of places that will certify that you (as an individual employee) aren't a bozo. Those don't scale terribly well, but worse, they also charge the job seeker.

You can make money but not do the world much good by charging (probably bad) employees a small fee to apply or charging bad companies a lot for dubious access. But while that's probably where the money is, it does the least good for the world of almost anything you could do in recruiting. Maybe a "schlemiel match-up service" for mediocre-to-bad companies with exactly-equally-bad employees? Don't know. I'll bet you guys wouldn't be passionate about that one ;-)

And yet, how do you make enough money and still scale well on matching up the best companies (who don't have to pay as much to hire) and the best candidates (who should never, never be charged anything at all)?

It's a hard problem. Glad you're thinking on it.