I agree with all of the posts complaining about the 4 hour limit.  I'm a member of many huge online forums, and this is the first one I've encountered with a 4 hour new user punishment.  It's not a very welcoming way to engage new users into the community.

How about an optional link to a 3rd party "trust service" - something like TrustCloud.  You could then allow users who have linked to it, and have above a certain "trust" score, to skip the 4 hour wait.