All of these news/information sites seem the same with a few exceptions.
Mixx homepage sorts by subject (Popular, Tech etc.), Digg and Newsvine were not anything special to me. Although, Newsvine's homepage is a bit much for me. They could do without some of the content to clean it up a bit. But that's just me... Reddit's homepage was simple, but almost too much so. It is almost hard to tell the stories apart because they seem very close together on the page.
I also noticed that the Reddit help lists four ways to use Reddit. The first one being, "Read: User-submitted links, it's more fun than being productive!" Ok, so isn't that right there the crux of the matter?! When do I have time to use these sites and do I care? Ok, so some of the more "news" content I find interesting, but I don't know that I need to read about all of it. And whatever happened to good ol' newspapers? Seriously. Is it is a good thing that people are stuck on their computers reading all of the time. They might be well informed but do they have social skills.
Ok, sorry about that rant. I think for me this is really about that I do not need 20 different service to bring me information and find web content I enjoy. What I am learning about some of the Web 2.0 tools is that we really need to pick and choose what we like and just stick to that. Otherwise, where does the rest of your life kick in? When do you eat? Exercise? Have hobbies? If I'm stuck reading all of the various information sources, I wouldn't have time to go for a walk (speaking of which, it's almost spring in MN!...) or cook dinner! So, can you tell I think that these tools are a productivity DETRACTOR?
That said--I am still struggling to figure out how to use these sites in a library setting. If anyone has any good ideas, put them on your blog. I'm going to start looking at what others have said, because I am drawing a complete blank.