Logic of a "free" customer

For the past few days, I have been thinking about how much is a 'free' customer worth.
For example, All the social networking sites like Facebook, Orkut, MySpace offer free logins for anyone. Similar is the case for eBay.

For example on eBay, all buyers are free registrants . Only the sellers pay - and that too when they get a product to sell. This gives rise to an interesting situation - without 'free' buyers, there are no sellers - and without the sellers the revenue model fails.

Similar is the case with Orkut - without the free users, there are no ads, and hence no money. But its slightly complicated here as Orkut is owned by Google. so there might be opportunity costs involved. like for example, when someone clicks on ads by google from a third party site, google must be paying something to that site as well (as it does in adsense). So when Google values its Orkut users, it will also factor in these savings.

Facebook epitomizes this type of revenue model - it allows advertisers to select their target group very effectively. Allowing them to streamline their ad via features such as
* Location
* Age
* Sex

* Keywords
* Education
* Workplace

* Relationship Status
* Relationship Interests
* Languages



But exactly how useful are these customers? there might be some customers who never click on any ads. Or for that matter, sell products on eBay. So these people never make money for the company. On second thoughts, these might still generate some revenue for eBay - by increasing the selling price through competitive bidding.


This thought cropped up in my head while listening to a presentation on the revenue models followed by browsers. Since then I have not been able to stop thinking about it. So HAD to publish it. Anyone who has some idea on this, please do comment/ contact me. I wish to learn more about this fascinating concept.