The 80/20-rule in marketing is history. In his book The Long Tail Chirs Anderson states that, in the internet age, 20 percent of the customers are no longer responsible for 80 percent of a company's turnover.
Anderson argues that products that are in low demand or have low sales volume can collectively make up a market share that rivals or exceeds the relatively few current bestsellers and blockbusters, if the store or distribution channel is large enough. Examples of such mega-stores include the online retailer Amazon.com and the online video rental service Netflix.
Here you can find Anderson's blog, and more information about his book.
Read the column here.