theres some good points but the key to social networks from my view is "niche marketing" if your selling "spoons" join groups in social networks that are selling "spoons" it's best to keep it simple and then expand.
So far, the people I've seen make the most money on social networks are eWhores and affiliate marketers. They make in the thousands a day and they don't have to write a blog. There are quite a few ways to make money off of social networks, not just blogs, microblogs, etc.