As someone who (relatively) frequently says things aren't hacker news, I think the most important distinction is with things that are actively harmful, such as politics, and often economics. They get people into heated discussions about something that isn't really relevant. Off topic things like "SF meetup" are a bit noisy, sure, but if done in moderation don't really hurt anyone.

We've always encouraged people to post about what they're doing, if they're looking for feedback. You should be proud of the work you've done, and not afraid to share it in appropriate situations.