Nice article Jeremy. My answer though is none of the above.<p>First, most social networks make just as much money off selling data as they do from ads.<p>Second, all the ads you mention fall into the same category. That is, the product being advertised potentially creates value for the user. So basically the user has to click on the link and buy the product.<p>The most profitable advertising is the type where the ad itself creates value for the user, in addition to the product being advertised. For example, music videos on MTV.<p>Unfortunately all of the social networks in existence today are monetized under the traditional model.<p>The startup I'm currently working on (kitchen table phase) is a social networking thing that actually allows users to manipulate advertising spatially in three dimensions. Of course the user's perspective is completely different, all they see is how the website makes their life easier (and gets them laid) and not how its being monetized.
When you have a lot of committed users that frequent its always possible to come up with strategies that dont involve just the normal advertising channels. e.g. suicidegirls sells branded merchandise and bebo is getting into parnerships with amazon and ebay. So this article is a bit simplistic and I think you could make $50m revenues with a lot less users than it dictates.