Heard of The Long Tail? Chris Anderson's Wired article, now a expanded into a book, explores:
The theory... that our culture and economy is increasingly shifting away from a focus on a relatively small number of "hits" (mainstream products and markets) at the head of the demand curve and toward a huge number of niches in the tail.
The popularity and power of blogging, as well as other social online media, fits squarely into this. The clip above, from FORA.tv, is a presentation by Chris Anderson explaining The Long Tail.
FORA.tv itself is a demonstration of efficacy of The Long Tail. It is something like YouTube for the thinking person (although that is slightly demeaning because FORA.tv's features trump YouTube's). Not exactly mainstream stuff, but it definitely has its niche. Would we have seen this in the pre-social media internet?