Mini Blogs? What Are These?

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I heard a story about a guy that made a bunch of mini blogs on varies subjects (niches), made between $1-$10 a day off each with Adsense, and ended up making about $2000 a month with the income from all his blogs. Does this seem real? How much content does a "mini" blog need? (A couple of pages or 10+ articles on one niche?) Does anyone do this? How does it work? If any of you have websites that explain this, link them please.