Current tilde defaults promote controversy
The default "activity" sorting means that topics which lead to a lot of conversation tend to get bumped to the top. It seems like, in the long run, controversial topics will end up drowning out topics where the link itself is interesting but doesn't provoke people to react with a comment. I find that a lot of the most interesting links for me on other sites are the ones with the fewest comments.
I think it could be worthwhile to experiment with different default sorting, or even different mechanics. For example, Everything2 has a feature where, at a certain rank, users are able to add pages to a "Cool User Picks!" sidebar.
The current solution, custom sort ordering, doesn't seem like it will scale very well. People will tend to vote on the posts they see; if most people sort by activity, most of the votes will go to the most active posts anyway.
Anyway, just food for thought. I don't think this is super urgent, but it seems like something that would be good to think hard about and get right in the long term.
I think the idea in the longer run is to allow for users to have custom defaults and to have the default sorting the rep-based voting method (which currently is just 1-to-1 but will eventually account for all sorts of positive contribution-metrics to try to weigh people's vote by their association with the ~ community they're voting on.
For instance, I've been active in ~talk and ~tildes but not at all active in ~tv (I generally don't watch anything). So my vote power would some day rise in ~talk and ~tildes assuming I'm not a complete tool, and my vote power in ~tv would be minimal.
That sounds cool. Hard to weight and moderate but cool.
The 'activity sort' was added here as a stop-gap while the site is small, to keep it from seeming inactive like most link aggregators in their infancy. Reddit used bots to auto-crosspost content from other sites when it was getting started, and so have a lot of their competitors when they started up. That seems like a recipe for garbage content, though.
Frankly, 'activity-sort' blew our expectations out of the water and killed that problem dead - it's a keeper. In the future, though, once this place is a lot more active, the 'activity sort' isn't likely to be the default for anything other than fledgling young groups just getting started. Eventually they grow out of this newbie-mode into something much more like reddit, with the votes/scores/weights determining the order.
It's likely that moderators might eventually be able to set the 'default' view people coming into their groups see for the very first time. I expect users will eventually be able to set the sorts up as they like for each group they visit, so a lot of this will also remain in the hands of the users themselves.
If we had sorting via comment and sorting via vote that could help as you'd have popular and interesting stuff and then the threads you could join for discussion.