>The solution was to split off new user groups into more specialized subgroups. The initial set of subreddits were effectively curated by Reddit itself, based on the categories of stuff that was showing up in practice. User-generated subreddits didn't come until later.

Everyone wanted tags for posts (myself included), and when they announced subreddits, there was a lot of belly aching. I thought the choice of using subreddits was a technical one to make the site more easily partitionable but they gussied up the reasoning behind the concept of communities. I think they made the right choice.