They could do a flickr-type model and charge only heavy users (say, more than 1000 friends) or charge for premium services (high-res photos or similar features)

They could do a flickr-type model and charge only heavy users (say, more than 1000 friends) or charge for premium services (high-res photos or similar features). EDIT: Even if social ads don't work out, I think Facebook will probably find a way to make lots of money. Although, maybe not enough money to justify the highest valuations we've heard.