Like other job sites, you will be able to set search criteria regarding a position (except salary level ?) and access the list of available positions. Where social networking features kick in is in the display of your degree of connection on LinkedIn to the poster of the ad (1 if you are directly connected, 2 if one person connects you and the poster through the network, etc.) and how many people have endorsed that person on the service. The whole idea is obviously to use your personal network to due diligence the company, the team and the person hiring, as well as find ways to get to them through your connections.
So who's hiring ? Obviously LinkedIn (which I recommend), but also Wondir, "which is building a new and different kind of information service to connect people who have information needs with the people and information that can help them". The person who posted the position is Allen Searls, Doc's son. Very cool concept.
Did I mention that posting jobs was free during the preview ? Definitely worth trying (10 jobs have been added since I began typing this post, and 360 within the first 4 hours). The combination of trusted referrals and due diligence, and what I would expect to be a competitive pricing (though I don't have any specific information), should make this service very relevant a number of positions.
This also hints at a source of revenues for LinkedIn, a question which has been floating around for a while. Charlene Li just added her insights on that very topic.