I looked at Digg, Reddit, Newsvine and Mixx. I frankly found the stuff at most of these what I would rate as lowest common denominator pop culture junk. Maybe I just looked at a bad time. I did find that I like the layout of the Newsvine page, kind of neat and like MSN's page. For content topic, I guess I would have to go with Mixx. I did join and recommend a story but found it had already been recommended and had 28 votes. The choice of topics at Mixx seemed to be more in tune to what I look for than some of the other sites. It's plainly laid out, but clearly divided by category topic and best of all uses fairly large print.
I can see how these sites might drive reference requests at the library. Things do seem to come to the top about which you might not know a lot and would be seeking additional information. Kind of like the trivia requests that come in via phone to settle a bar bet, if you've ever had those. Seeing how many votes a story has might be a way of deciding whether or not there is enough interest in a topic to add a book about the subject to your collection as well, even though it wouldn't necessarily be your patrons who are the respondents.
I also signed up for StumbleUpon which seems to let you be a little more specific in defining your interests. That one lets you click the stumble tab and brings up something you might like and so far based on my input hasn't been wrong yet. It's brought me some humorous pix of cats, a diagram of a cat brain (fun) and clear instructions for creating a self-watering device for the garden, among other things. So far it's been entertaining and instructive. I think I am going to continue to enjoy that. I chose it mostly because that is how I have often found nifty stuff, I've just "stumbled upon" it.