Interesting idea. Instead of simply saying people can't post if their karma is too low you could take the users total Karma relative to 0 and add a sorting feature filter that sorts based that. Only problem is new people would get buried pretty quickly and it may feel like they are trying to get someone's attention from across the room while in the middle of a pack of screaming monkeys. Adding a sort by "new" feature could help new users get their voice heard and voted up or down accordingly. Just a thought.