December of last year we had a huge influx of people come over from reddit. Literally thousands in one day. Many of them posted crap, but I didn't see much of it because I wasn't "following" any of them.  I should mention that many of them are still around and post awesome content and the meme posting people got bored and left. insomniasexx once used the comparison to twitter. There may be millions of people using the site, but my feed just has the content of the people I follow. So if my twitter feed is full of garbage, then shame on me for following crappy people/tags.
Where it could get interesting is in comments. Shortly after that influx of people we introduced the "ignore" and "mute": If you ignore a user, you don’t see that user’s posts anywhere. If you mute a user, that user cannot comment on your posts. You can ignore, mute, or both.
I haven't had to use these functions since that influx, but they're there to specifically protect a users experience.
I can say that we are in NO WAY interested in growth for the sake of growth. We don't care about pageviews etc. We are about providing a place for the thoughtful exchange of ideas/conversation. If Hubski grows to hundreds of thousands or even millions of people and we can keep the integrity of the content and conversations... great. If not, then we aren't interested in it and we will do everything we can to maintain what we think makes this place special.
We love this place and we don't want to fuck it up ;-)