You can spam to cheat both systems - 4 spams a day for 28 days gets you 100%, or 10 spams a day for 100 days for 1000 posts.

If you were going to go by posts, then something like 5000 should be the minimum, I'd say. 1000 is far too easy to get too.

In fact... there's a question - what happened to the ads that used to be at the bottom of the main page? The little text links...