What are social bookmarking sites? Basically, these are sites that allow users to post their favorite sites, using tags (or keywords) to categorize and organize them; then other users can take these bookmarks and add them to their own collection or share them with even more users.
Digg is social bookmarking and social networking gone a little crazy due to the fact that anyone can submit a Digg (site), and then anyone can comment on those same Diggs. For me the most interesting feature of Digg has to actually be the comments on the sites and stories, since the Digg community is not shy about letting folks know how they feel about a particular Digg. Primarily focussed on geeky, technology-type items.
Reddit is a social bookmarking Web site that works much like Furl and del.icio.us: you register a username and password, and then start submitting and sharing your bookmarks. Reddit is similar to del.icio.us in that users are encouraged to vote on the links and stories that they feel are deserving of being in the top dog spot: it’s kind of a popularity contest, so to speak.
The beauty of StumbleUpon, to my mind: you are able to take advantage of a vast network of dedicated Web searchers who are finding utterly brilliant sites and sharing them with you. I do have to warn you, though – StumbleUpon is an incredibly addicting way to search the Web. I found myself up till 1:30 AM one weekend, blearily clicking the Stumble! Button over and over again, because the quality of the sites are just so amazing; you just keep on coming across stuff that instantly merits a bookmark of your own.
At Newsvine, you can read stories from established media organizations like the Associated Press as well as individual contributors from all around the world. Placement of stories is determined by a multitude of factors including freshness, popularity, and reputation. Contribution is open to all, and editorial judgement is in the hands of the community.