I moderate a forum but not this one. This is what I do:
All new users have their first several posts placed in a queue; a moderator must manually approve those posts before they become public. (This keeps out obvious spammers - if a first post is spam, the user is immediately banned.) After a few approved posts, users are automatically 'promoted' so that their posts appear immediately. If I'm not sure about a new user, I change their status so that a moderator must approve _all_ of their posts.
Any time a user becomes a problem, I change their status so that a moderator must approve all their posts. If I feel the need to edit or completely delete a post, I start a PM with the user and we talk about why.
I almost never ban a regular user; rather, I let them post, monitor their posts, edit or delete as I feel the need, and if they're going to go away, they do it on their own.
Just another data point to add to the discussion here.
-S-