Tonight was yet another sold out social networking event — it was IBD Network's Under The Radar. The CEOs of LinkedIn, Spoke, ZeroDegrees and VisiblePath all presented their businesses. Esther Dyson of Release 1.0, Pradeep Tagare from Intel Capital and I were on a panel to discuss their respective business models. Based upon what I heard this evening, here is how I would sum up the different companies' business models.

LinkedIn — subscription (eventually) service to input and manage one's own contacts to search for connections.

Spoke — deeply integrated enterprise solution extracting contact data from enterprise applications (e.g. Outlook, Notes, etc.) to establish and leverage connections.

ZeroDegrees — Outlook plugin and related service to input, manage, prioritize and search connections.

VisiblePath — social networking software engine for prioritizing and understanding connections for integration into traditional enterprise software applications (SFA, CRM, etc.).

If you're thinking that they all sound pretty similar, I'm with you. These companies have way more in common than not. After the companies presented, the panel and audience voted on what they believed was the most interesting business. The audience preferred the model described by Ben Smith of Spoke, while the panel collectively preferred the business described by Reid Hoffman of LinkedIn. Interestingly, both Spoke and LinkedIn announced at the event that they had recently come to terms on financings — Spoke wouldn't yet say from whom they were raising money, LinkedIn announced that it will be funded by Sequoia — whereas ZeroDegrees and VisiblePath remain angel funded.

One thing that did surprise me tonight was the percentage of the audience who were users of LinkedIn. By show of hands, the LinkedIn members outnumbered the Friendster members by over 2 to 1. It looked like two-thirds or more of the audience had signed up to LinkedIn. Those are pretty surprising numbers. Of course I don't think there is another audience in the country that could replicate those statistics, but it tells you that the Bay Area entrepreneur community has bought into social networking on some level (either that or Reid had packed the audience with a couple hundred of his closest friends). It will be interesting to see how that scales beyond the Bay Area.