It's an emerging rule of thumb that suggests that if you get a group of 100 people online then one will create content, 10 will "interact" with it (commenting or offering improvements) and the other 89 will just view it.

The numbers are revealing: each day there are 100 million downloads and 65,000 uploads - which as Antony Mayfield points out, is 1,538 downloads per upload - and 20m unique users per month.

Consider, too, some statistics from that other community content generation project, Wikipedia: 50% of all Wikipedia article edits are done by 0.7% of users, and more than 70% of all articles have been written by just 1.8% of all users, according to the Church of the Customer blog.

Bradley Horowitz of Yahoo points out that much the same applies at Yahoo: in Yahoo Groups, the discussion lists, "1% of the user population might start a group; 10% of the user population might participate actively, and actually author content, whether starting a thread or responding to a thread-in-progress; 100% of the user population benefits from the activities of the above groups," he noted on his blog in February.