Earlier quoted context omitted.
Karma >= 2 would probably be sufficient. It rules out people who have not interacted with the community at all, without turning HN into some exclusive "members only" club.
I think it should be at least karma >= 50
What happens if this guy heard from someone that people here give good feedback abt his new idea or startup? Should he wait for long (like 2-3 weeks to get 25 or 50 points) to get feedback? So I'm a bit biased about having posting thresholds for new threads.