50% of all Wikipedia edits are done by 0.7% of users
1.8% of users have written more than 72% of all articles
If we also add evidence from Bradley Horowitz that roughly 1% of Yahoo’s user population starts a Yahoo Group, we seem to have The 1% Rule: Roughly 1% of your site visitors will create content within a democratized community.
I haven’t analyzed all of Front Porch Forum for this, but when I looked at our flagship neighborhood forum awhile ago, we saw 90% of the neighborhood subscribed and 50% had posted in the past six months. FPF’s design encourages a very high level of participation from the general public.