It�s a concept that we all learned as tykes in the sandbox with our first red wagon or dump truck: it�s good to share. Now, in this fanciful web 2.0 future (though I�m not yet convinced that web 2.0 has grown up all that much since kindergarten), sharing takes on a whole new meaning. A host of social bookmarking and networking services allows anyone to save, post and describe links publicly and amongst their friends, on sites like del.icio.us, Ma.gnolia, Digg, Facebook and Newsvine. As we prepare to rethink the story pages that make up the bulk of msnbc.com, we want to know how our readers use (or don�t) these types of social sites. Most sharing sites have sp