Think Wikipedia. It's been interesting to me to watch Encyclopedia Britannica and World Book move from selling $1200 book sets to $9.95 online subscriptions. While that was happening Wikipedia emerged in 2001. By 2005 Wikipedia had nearly half a million articles, more than a million articles in 2006, and 2.5 million articles today. World Book has 1.3 million articles online, and the Britannica site doesn't give a number (that I could find) but Wikipedia says Britannica has 120,000 articles online.
Another example is iStock photography that allows amateur (or professional) photographers and illustrators to post their work for others to download at a tiny fraction of what stock photography houses like Getty and Corbis charge. Prices at stock houses have gone through the roof in the last several years. There once was a difference in quality between what you could get from the stock houses and what you can find online but the gap is narrowing every day. The stock houses are going to have to find a way to stay relevant and competitive.
Another example of "crowdsourcing" even closer to home: last month I posted several possible designs for the cover of the book Wine Savvy to draw on your collective wisdom, a decision generally kept internal.
Earlier this week Joe Wikert wrote about a new service HarperCollins recently launched called authonomy. It is a community site for authors and editors. Authors can get feedback on manuscripts. Other members read, review, and rank your work. Editors and publishers can scout new talent and ideas. I don't know how this site is going to go over, but I suppose this could be "crowdsourcing" the role of the agent, or at least talent scout, or at least "peersourcing" some editorial development.