Anecdotally, I've always asked subreddit owners/mods I've met about this. Turns out many of them obsess over stats just like Steve and I used to (and shortly thereafter, Chris, who built our first real-time stat engine that was both blessing and curse because of how we obsessed at times). The more we could do to make redditors give a damn, just like we did, the better things got.

Steve is one of the most reluctant feature guys I've met and while it's frustrating at time for a guy with too many ideas like me, it's so important to know what not to build into a product -- it makes him such a great programmer. So creating a subreddit was dead-simple. No bullshit. The hard part was going to come (actually growing it) and we could still do more to encourage new subreddit owners and give them tools to help get the word out (we've long promoted user created subreddits using house-ads that I'd design, but that doesn't scale). There are even subreddits like /r/newreddit that redditors made to promote, you guessed it, new subreddits.

So - 'buy in' for subreddits was in part by setting the tone well with the ones we created, like /r/programming, before it was open to users -- this created an unintended air of importance the day we launched it. "Subreddits: now not just for co-founders to create!"

I've been really impressed by local subreddits of late, esp in surprising markets like /r/Grandrapids for instance - there's something awesome happening here: http://www.reddit.com/r/grandrapids/