Threads that have been created/replied to within the last 90 day will get bumped to the top based on last reply like normal, but if a thread hasn't had a reply in 90 days, it will need 3 replies to get returned to "active" and bumped to the top. It will keep getting bumped to the top based on last reply until the next time it goes 90 days without a reply. People on the thread will be notified, but it won't get bumped to top unless you get the other 2 additional reply's.

I noticed some confusion about this feature and I just wanted to clarify this.