1) The problem is not "new user" the problem is "new users." It's not a feature I'd use all the time, either - but it's a feature I'd like to have for, say, yesterday. 2) Hubski heavily emphasizes personalization - I think (but obviously cannot prove) that it's far more likely to have a user with an account that doesn't comment than a non-user who suddenly signs up. I can back that up with a little data; I see lotsa lotsa users that pop up and follow me, but when there's a Reddit wave, they usually start commenting pretty much immediately. 3) If they're doing anything other than sending a PM, their comments will be visible in threads... the person they're responding to (assuming they're ignored) simply won't get a notification. That's the thing about "ignore" - it's much less of a behavior shaper than people think.