Is google starting to crack down on this? My theory is how in the world can they if an article is over 30 to 35% unique. Not all content on the web can be 100% let alone 70% unique. People take content and change it around all the time so I can't imagine google figuring this one out, particularly if the articles are adding some sort of value the to web in various ways.
TIP: If you keep your forum posts a little shorter, those with the lease patience have a tendency to ready through them;-). Unless it's a great story or post.