FranticFish - 9:28 am on May 26, 2010 (gmt 0)
showing the URLs after a certain number of posts
Uh-uh. Please. No. Not unless you want to see thousands of 'me too' or 'great post' responses.
Anything based on post number encourages people to post no matter what.
I've seen a system where only posts over a certain character number were counted as a post and quick responses weren't. Still not ideal. The level of attempted spam might well go up from people cutting and pasting articles to start threads, and some short posts are very useful.