You're about 7 years late. Job sites are on the decline and are losing ground to niche sites like 37signals' job board and social networking sites like LinkedIn. Going with a free-to-post model isn't bad if you're a niche site (e.g. one that specializes in jobs for developers) because it allows you to gain critical mass fast. Then you can charge. But for a generic job site, this is a recipe for disaster. No differentiation + No Revenue Model = Fail.