This is a place to collect CommunityBuilding success stories!
Did CommunityBuilding help you solve some real problems you faced in the context of your own online or real-world community? Are there some questions & answers that led to significant improvements and achievements for your community? Any ideas developed on this site that have been useful for your own community? Then add your story in an answer! (One story per answer, please!)
Disclaimer: the idea for this thread has been taken from MathOverflow.