I’m a bit ambivalent about transitioning from a (admittedly archaic) maillist to a dedicated forum system.
I expect a major activity level change because of the difference between push notification and pull. Every time someone posted to the maillist, inbound mail reminded me that there was activity to read. But so far, it looks like I must actively seek out the Discourse site and then (painfully) seek out the activity.
And while new users will have the benefit of seeing subject based threads that might address their question, it will quickly become overwhelming to look through. (Although perhaps better than the maillist Archives where the subject data is masked by generic calendar-based labeling.)
I also have little reason to make visiting a Discourse site part of my daily routine. Although I absolutely DESPISE Facebook, it has enough other content so that it drives traffic. Plus I receive notices on every thread where I’ve posted previously.