I submit a different approach. Instead of targeting large sites with plenty of users, why not mention Hubski in smaller more intelligent, forums and sites. Places where you know the people are quality. Quality over quantity. That, I think will keep the site what it is for longer.
There are plenty of places for the trivial. However I think it would be a poor design if we could only keep Hubski quality by keeping it small. If you are only experiencing Hubski through the lurk page, what you see and what I see are somewhat different. You might want to follow a few people or tags that you appreciate, and give building a feed a try.
All this said, I would be really glad to know about where you might suggest we focus our efforts aside from the mainstream social media sites? I'm all ears and I agree that this might be a better approach. I have mentioned Hubski on TED forums in the past and it seemed to bring some great contributors to the site. I have also done this in NPR forums, but beyond that I don't really know where else I could do so? I'm all ears and I couldn't agree more "Quality over quantity". -100%! The most effective word of mouth is from you to a friend though. Thats been my experience. Thanks for the comment, see ya around!