I like the idea, but I think the main issue is design. It's pretty hard to figure out what's going on, and the interface is inconsistent. Example, on a user's page, each link they posted isn't in the same position, they're staggered down the page. That makes it difficult to scan someone's posts to find something interesting. I would say if the posts are going to have images, make sure they're all the same size, or maybe have them float right so all the link titles are aligned left. In the same vein, each user has a different size/shape avatar, they should all be, say 48x48 square for example. There's a lot of those little details throughout the site that doesn't make for a great user experience.

Also, I think you need to switch the focus to reading, as others mentioned. Interesting content is what's going to get people coming back. So the front page should show the most popular links instead of people. I actually think this page (http://www.howl.com/explore/all) should be the home page. I think that would make a much more compelling first experience, and you should be able to get there without needing to sign up. It's simple and you instantly get a feeling for what the site is.