Everyone should probably "get" this but I'll enumerate.
Social aggregators become, whether you want it to be or not, an advertising platform.
Now, I'm not saying, you will have some flash ads or have paid content or anything. What I mean is, when your user base gets to a size where it has some ability to drive traffic to another site, and make them advertising revenue, then sites will come to hubski and make posts to drive traffic to their site. This happened to digg, and reddit, but not so much to slashdot in the early days, because the curator model of slashdot meant they tried to be a bit fair about how many times they linked to any given site.
So anyway, you're driving page views on someone else's site, they're getting advertising revenue, it's costing you to handle all those page views and clicks and comments, and you get nothing, they get all the benefit.
So that sucks. Yeah, I don't have a solution either. What can you do? I mean, you need to allow links off site otherwise whats the point.
I read Kelinbl00's post about corporate structure. What did you guys decide? Did you look at becoming a BCorp? I like your intentions, both mk and thenewgreen, you both appear to want to build a lasting community that values quality over quantity, but if you cultivate the quality, quantity WILL come. Quality attracts quantity. :-)
Ultimately, I don't think Reddit or Digg or whatever failed just because of their size, I think they failed to lack of transparency. When you get to a certain size, you start to think that you must have some insight on the best way to run things, so you go off and have a "deep think" about how you're gonna handle a situation, make a decision, and then you might as well have just flipped a damn coin because half the time the community is going to think that decision is wrong.
Transparency of and participation in the decision making processes, will obviously make things longer to decide, but I think you'll be better for it in the long run. Being a BCorp and codifying that process into the charter of the organisation might be worth doing.
BTW, for a site that would replace my daily fix of news and opinions, I'd happily pay a few dollars a month. I'm not a huge fan of micropayments of indivudual features etc, but you know, it would be very easy to calculate to within a reasonable margin of error, how much compute a given user "consumes". Just having a dollar figure on the profile page saying "In the past 30 days, you used $1.50 of hubski's resources wasting time on this site" might guilt me into sending you some money every month to cover the costs. "Links you have posted used $5.60 worth of resources" ... you could keep track of the stats and figure out which users are driving the most traffic and if they're driving them off site to their own blog, then send them a bill. Hahah, just kidding...
Add some certain percentage to cover administrative costs, etc. I mean, I think if the site got big enough and the discussions were getting to the point where they were insightful as shit, and you guys wanted to make it a full time gig, then it's not unreasonable to add enough "administrative overhead" to support that.
Meh I dunno. It's a DARPA hard problem. Otherwise someone else would have nailed it by now. But it doesn't mean it's not worth solving.