IIRC, the default subreddits do have mods, and a lot of them at that. So there really isn't absolute freedom except in new subreddits where the population is small enough to contain would-be delinquents with downvotes. This site also has a small population and even smaller divisions, and at this point remains largely untouched by annoyances. But how can we, as a community, prepare for a future where the scum of sites like reddit come here? Mods can be used to stave off the crazies, but copying the mod system from other sites could just push it towards the same ill-fated content that we left.
I think that what might insulate hubski a little bit from the proliferation of trashy content is the lack of karma. The culture, it seems, is more about sharing than narcissism, and the structure of the site reflects that. The promotion system is fuzzier and more obfuscated than reddit's, and that makes it seem more genuine. I do think that moderation of hashtags over time could become an issue. With the ability to only attach one tag to a post, the really big tags like music, science, technology, news, politics, etc. will eventually get bloated. A potential solution is to strictly limit certain hashtags, or possibly automate the worst offenders. For example, if image memes were to take off here, they could only be posted in the #memes tag or risk deletion - and the tag would be autosuggested when the site parses the quickmeme url. That could be used to keep certain hashtags more 'true', without the need for multiple tags with varying degrees of purity (/r/gaming, /r/games, and /r/truegaming).
I guess since this site revolves around following, anyone who would be banned can just lose their voice altogether if no one follows them. I really hope that this holds out because it already looks more promising than reddit.