What I am saying is that ad-based businesses aren't stable enough to warrant the valuations that we're seeing right now. The core audience - the user - is not loyal enough to justify valuations that would take years of sustained behavior to see any ROI.
The cause of Friendster's demise is irrelevant - it's the speed at which it happened that proves the point. 19 million users lost in under 2 years is fast even for web apps.
Ads are a perfectly legitimate form of revenue.