Making The Cash Register Ring on Socianetworking

We know that Linked In and Facebook have received huge cash investments from venture gurus. How do these sites actually make money?

According to Advertising Age, http://adage.com/digitalnext/article.php?article_id=127817, Linked In, top professional site, generates revenue in four ways, and is about to add a fifth:

Here's a Model for Profitable Social Networking
There's been a lot of talk and advice on this blog about how social networking sites will make money. One major network, LinkedIn, is using a variety of models to drive revenue, which amounts to $100 million a year, according to ...

How can participants and members generate financial benefits? Write and share how you've used socianetworking/sociabiz networking to enhance your business or practice.

Would you like tips on how to up your ROI on these sites?