A better tagline than "Hacker News for researchers" might be "Crowdsourced Faculty 1000". Either way, I wish you luck, as getting a critical mass of engaged users in this area is a very difficult task.
So many people do read and review papers, but then those reviews are just kept in a private file somewhere (or just in their brains) and hardly anyone sees them. So much great insight into published science is lost to the public this way. Lately I've been trying to blog about papers I read and then share my blog posts with http://www.researchblogging.org/, but even that isn't a very common thing to do.
If your site could become a hub for this type of discussion, it would be wonderful. Do you support (or plan on supporting) a researchblogging-like trackback system, in addition to comments? That might help you gain publicity too, if popular science bloggers link to your website when they discuss a paper.