In reply to Elizabeth Brown.

Elizabeth, yes the closest we seem to have to this at the moment is either
search, or the related items in Friendfeed (which is only triggered by a
common link) or shared tags and links in bookmarking services. One of the
things I've always liked about the PubMed web site was the "related items"
button which I found to be a good way to be more confident that I'd caught
everything relevant.