I would argue that you've come at this problem from the employee side (ie, "I have a job but I might jump for a better job - someone should make a website for t

I would argue that you've come at this problem from the employee side (ie, "I have a job but I might jump for a better job - someone should make a website for that"), but the employer side is where you'd be better off spending your time. There are less employers than employees and they have their resources spread more thinly. For them, I think quality, rather than quantity, is your main value proposition. The neat thing about already-employed potential hires is that their employment is a kind of social proof. They were hired at X, therefore they must be pretty good. How about this: take signups, but ask them for their current employer and their field. Now an employer can say things like "I want to poach employees from [Google,Apple,Microsoft] in Engineering" and have a place they can do that.