from BBC News:

Just 10% of Twitter users generate more than 90% of the content, a Harvard study of 300,000 users found.

How is this even remotely surprising?

Isn't this consistent with millions of other scenarios in life?

This 90/10 ratio follows the basic theory Joseph Juran coined for this phenomenon back in the 1940's, after the Italian economist Vilfredo Pareto.

via Wikipedia:

The Pareto principle (also known as the 80-20 rule,[1] the law of the vital few and the principle of factor sparsity) states that, for many events, roughly 80% of the effects come from 20% of the causes.

This is not to be confused with Ms. Jackson's Pleasure Principle.