When I discovered that you could type "define:anyword" into a Google search box and get a definition, I pretty much left dictionary.com behind forever, except for the occasional thesaurus lookup. The new Wordsource works similarly - you type http://word.sc/anyword in your browser and get your definition.
Wordsource, however, defines itself as a social dictionary. Anyone can tag a definition and upload pictures to associate with the word. Strangely, they're even encouraging people to attach their own pictures to the word "genius". The definition page itself has several useless facts at the bottom of the page, along the lines of "x people like/dislike this word", "x people can say this word 5 times fast" and "x people think they are this word". I'm not sure folks who regularly use dictionaries are really interested in frivolity with their definitions.
I think the social aspects here are forced. Gimmicks don't make a community. I'm not even sure calling this a social dictionary makes sense. If you click on a picture, you view that person's profile (even, apparently, if they've uploaded a picture describing the dictionary entry). There doesn't appear to be any way for people to gather or actually interact.
Wordsource does have one really nice feature - the ability to look up words "starting with" and "ending with".