[alltakendamned]

How about when people return to your service, you just show them a little icon somewhere that tells them they have new replies to comments they made. And then when clicking on that, you get to see the relevant comments or threads ? It notifies them without being intrusive in any way.

I mean, I personally attempt to prevent any kind of "push" or "reminder" of happening, because that is to my benefit, but it might not benefit the engagement on your server. In essence, push is bad, pull is good as I see it.

Then again, I'm most certainly not the average technology user, so take my thoughts with a grain of salt.