A very interesting concept being created is called “We are smarter than me”
“Over a million students, faculty and alumni of the Wharton School of the University of Pennsylvania and the MIT Sloan School of Management, as well as leaders, authors, and experts from the fields of management and technology were invited to contribute in a wiki-based community that coalesced at wearesmarter.org. Members were asked to develop and share their insights about why community approaches work or don’t work when it comes to marketing, business development, distribution, and more, and what companies have to do to make them work better.

The goal of the project was to develop a book that addresses what other best-selling books on community have not. Wikinomics and The Wisdom of Crowds have identified the phenomena of emerging social networks, but they do not confront how businesses can profit from the wisdom of crowds.” (cf wearesmarter.org)

What we can discuss is the efficiency question. Of course, a collectiv and collaborativ writing must be faster in terms of quantity and ideas but is it really efficient? To my mind, a book must be a synthesis of a thought and not an addition of many.
The collaboration is fantastic but need to be “controlled” by super-readers to make it coherent, usefull and affordable in terms of content. Have a look at wikipedia: there is a team of moderators who help keep it corrrect, as much as they can.
Anyway it is a very good experience and a very nice way to do things and improve the diversity and the quality of a book.