A large part of Reddit winning was Kevin Rose fumbling while CEO of digg. Reddit had open sourced its code by then, and Digg didn't even bother adding some of the useful functionality.
I really expected them to copy user-created subreddits. They'd had a critical mass of users at that point, so whereas it took a year or so of me seeding new communities, doing house ads, and generally hustling subreddits -- they could've been up and running with a myriad of healthy communities.