Instead of subreddits, you follow users and tags. When you upvote posts, you share them with whoever follows you.
It's sort of like a community web of trust. It works really well.
I'm not really sure how that would work in a site where the conversations are focused around specific users.
1. Things are democratic overall. You tend to follow people that share things that you like. You see what they post AND what they "upvote". Whenever someone votes on something, it also shares to their followers. Combined with some weighting on how popular a post is, and how recently it has been touched by someone else, this effectively means that you get a list of posts relevant to your interests, sorted by popularity. Any one person leaving would have negligible impact on your feed's content.
2. You also follow topic tags.
I don't really use them so I can't do a good review.
I had some more bookmarked but can't find them at the moment.
lobster at_sign laro DOT se
For some reason I can't reply to am1988 but maybe he's right, I don't know.