I find it is really helpful to write answers to questions posed by others - and to compare my answers with them. Also useful discussions in the comments, help to clarify ideas.
So much better than wikipedia for controversial subjects. Get people writing as themselves and not having to put everything into neutral terms.
And - it promotes respect for others points of view. Anyone's opinion is valid, and only they can edit their own articles.
Kudos to those who created Quora!
Many of my answers here eventually end up, worked up a bit and polished, as articles on my science20 blog Robert Walker's blog