I use reddit to stay updated on major topics in the more intelligent subreddits -- timely things like news and current events, scientific discoveries/breakthroughs, and modern politics. Hubski seems like a community more involved in a larger variety of interesting topics found around the web, less concerned with concrete events and more interested in thoughtful articles ("a thoughtful web" is a fitting tagline). I like Hubski because it hasn't developed a singular "voice" (yet; this still remains tentative). It is still developing a personality, and its members are still testing the waters. Personally I hope this period of Hubski's development lasts as long as possible, but realistically I'm not so sure how sustainable it is.
Just to let you know, this issue is very important to me. Actually, it's probably my biggest goal/concern. That's a part of why I just pushed this update: http://hubski.com/pub?id=5046 Let me know if you think we are slipping. :)
Personally I've never been good at (or fast enough) to find and post links since I don't want to spend my day digging through endless rss feeds and irrelevant google alerts - I just want a site that has all the good stuff already posted - so I'm a little wary of the "power user" format here, however, as long as the content is good, I have to say I'm already sold on the idea of Hubski.
Oh, and great job with the site. I especially like the clean and simple layout
My hope is that there will always be a competition to be the most interesting content sharer. If an echo-chamber begins to form, hopefully there will be those that will maintain hubs that run counter to it. If you only follow these people, you should be able to escape the chamber to a large extent. Comments may be another issue, however, and I think creative solutions might be required there eventually. We'll see.