Disclaimer 1: I work for RealContacts
Disclaimer 2: my last coding was ten years ago in C++, so have mercy

I'll try to talk about the issues rather than make a shameless plug. Thanks to Abbi for this good article and to the readers for bringing up our service.

In terms of usage, we have users in 17 countries and over 400 employers using the service.

But Tandel's point is right - if you come to the site having not been invited by an existing member, you have to build your network out. That's easy for employers and recruiters, who post a job and send it out to their contacts and employees, who forward it outwards. For job seekers or people helping their friends, the idea and hope and gamble is that someone in your network will eventually connect to or become a source of jobs. Stanley Milgram's Small World and Mark Granovetter's Strength of Weak Ties ideas support this, and our experience to date does also. You can read about the background science here:
http://jobs.realcontacts.com/science.asp

To protect privacy, your identity is only know to your direct contacts, but your opportunities, searches, and notification preferences reach out in a codified way to your extended network.

We'd welcome feedback and ideas, whether directly via our site or through this forum.
Gary Franklin
info@realcontacts.com