According to recent data in most online communities, 90% of users are lurkers who never contribute, 9% of users contribute a little, and 1% of users account for almost all the action.
1% of users participate a lot and account for most contributions: it can seem as if they don't have lives because they often post just minutes after whatever event they're commenting on occurs.
9% of users contribute from time to time, but other priorities dominate their time.
(According to some things I've read these people primarily participate by commenting on content created and uploaded by the 1%)
90% of users are lurkers (i.e., read or observe, but don't contribute).
This was first formulated by Jacon Nielson but research by Bill Tancer author of Click supports this out as well.