This type of site was new to me. I looked at all four -- Digg, Reddit, Newsvine, and Mixx. There was no clear winner in my mind. Reddit lacked pictures. It's list format was just too "plain Jane" for me. For me, it was a tossup between Mixx and Digg for straight news sites. I chose Mixx only because in the Entertainment category they had a subcategory for books. I searched for books as a tag and had very mixed results. I also registered at Newsvine because I liked the look of the site but I am hesitant about becoming a columnist. This blog is enough writing for me.
I added the same article to both Mixx and Newsvine. The article is from Reuters and is about Mills & Boon publishers. The title is "30,000 Kisses and Steamier Than Ever." I know that when I was in my 20s and living in rural Minnesota (far away from the nearest bookstore) I subscribed to Harlequin novels through the mail. It was interesting to read about the changes in romance publishing now that I read many fewer books in that genre.
Right now, it feels like this sort of a site is a productivity distractor more than a productivity enhancer. I'm already reading general news sites and blogs. I'm not sure I want to add another source of daily reading. I haven't yet explored enough to see if there are educational used for these sites.