There are several fundamental differences between reddit's content-sharing system and hubski's. (One of the biggest things hubski does that reddit does not, allowing both original text and an external link in a submission, is I think an underappreciated reason for their differences. That and the lack of a "downvote.")

They are both "aggregators" in the sense that links from all over the net surface in both places, but they serve very different purposes. hubski is more personal, more personalizable, and a bit harder to use. Its interface is not clunky, but certainly less fitting to mass use, and I think that will go a long way in turning aside any sort of mass influx of users. (Yes, there was one today, it seems, but give it a week or two.) My point is that while hubski resembles a young reddit in, say, "intelligence level," it does not have many other similarities and shouldn't decline for the same reasons. I just can't see it becoming mainstream.

I've seen lots of talk on Reddit recently about the "Death of Reddit", and how the site has become inundated with increasingly low quality content as the audience has grown.

Incidentally, I see this argument from time to time, and I can't stand it. As the amount of low quality grows, so does the amount of high quality havens (subreddits). I could name a dozen without stopping to think. The problem arises from considering reddit one website. It's not. hubski is. Another fundamental difference.

EDIT: with all of that said, I've just been contemplating unfollowing #askhubski after reading my feed, which it currently is 80% of. What the hell is it about reddit that is a magnet for a lot of stupid, banal questions? It's been less than hours since that thread was posted and already we've got askreddit 2.0 pouring in. I thought theoryofreddit subscribers generally knew better than that crap.