I had ocassion recently to discuss the "1% rule" with a colleague, in relation to contributions to an on-line community of practice. My colleague professed to not having heard about it before. The hypothesis is that if you get a group of 100 people online then one will create content, ten will "interact" with it (commenting or offering improvements) and the other 89 will just view it. The key point is to look after your content creators, for they may be a rare species!
I first read the article in the Guardian Unlimited (July 2006) – should anyone wish to challenge the statistics!