Ok I've changed the plugin. It now will not show posts with a karma level below your threshold but it will show posts with a karma of 0...ie new posts or posts that have no rating, this is needed so that new posts are visible.

I've also added username filtering as an admin option...I have it working well.

The only issue I can see is that you lose thread context if a big chunk of posts disappear but if you aren't interested in what a certain user has to say then that won't bother you anyway.