I can attest to this being true of Hubski, as it is with most any other aggregator. As you can imagine, when we started Hubski we invited all of our friends to use the site. That's really who the first batch of users were. I have a number of friends that I never see on the site that will tell me in person that they visit Hubski regularly. They treat it like they would any online magazine and just consume content. I'm always shocked when people IRL reference a story or conversation on Hubski that they didn't participate in. Some people just aren't interested in participating but they still enjoy consuming new information. I don't think there is much that can be done to change this. It's only a factor because we have a small (but growing) community. If we had 100k people instead of 10k no one would even notice. But, if you are able to solve the problem of how to get lurkers to feel comfortable in actively engaging, well... you should patent that snake-oil and make a fortune.