There's an interesting thing about scale.... At 40K subscribers (collected over 15 years), my subreddit is pretty small niche. I tried duplicating it on the Digg reboot last year (yes, Digg sucked, sucks, and will continue to suck for the foreseeable future, but it was an informative experiment anyway)... because the niche is so narrow, and the Digg user base was so small, it never flipped over into growth mode. I'd promote it, get a couple of posts and a couple of subscribers, then crickets. After several rounds of that I walked away from new Digg. Meanwhile, on reddit with its billion+ users, 100 million+ active daily, the narrow niche continues to grow and because it has enough content contributing users, it's not my personal soap box, it's a truly user maintained community. But, that 90-9-1 rule definitely applies, probably even more skewed in my experience: 40K subscribers, probably less than 40 occasionally active content posters - an average of maybe 4 new posts per day, but... 40 posters are enough to keep the 40K engaged and growing.