Not to say that FB is going to be as big as Google. Outliers on that scale may only appear every couple decades. But they have a similar hackerly vibe.
Couldn't the same apply to Linkedin?
In a way all the attention is on facebook, linkedin is getting as much attention as google did in 2000.
Online Newspaper X has over 20m online readers. Most of them have at some point subscribed to print publications @ $200+ per year. If it was a membership site at just $2 per month, wouldn't they be able to keep some readers? 10%? 5%?.
You're not telling me someone making $80k per year would replace the newspaper she reads every day to to save a few cents a read?
Wouldn't people pay to use google? What if it was just $0.50 a month? or $0.01 per search?
The concept that if people use a site, it's worth money, has not proved itself.
World of Warcraft takes in 12.99 - 14.99 per user per month and has approximately 10 million active subscribers. Plus additional profits whenever an expansion comes out.
http://www.mmogchart.com/Chart1.html
faq...
[EDIT: added "per month" to second paragraph, first sentence]
Granted, being able to monetize doesn't matter to your users, but if you keep running through your VC, you eventually can't keep up development at the same pace.