Just thinking out loud. What if you had crawler/monitor that recorded a daily snapshot of the popular items or front pages of the big social media and blog sites: digg, reddit memeorandom, slashdot, gawker empire, etc. Pull the links and stories out and record what the blogosphere does for 30 days around those stories, but don't publish anything. 30 days later, summarize and recap to give a delayed release retrospective. Rinse, cycle, repeat every day providing a continuing look back at the real(?) impact of the socially selected items. Provide as service and get rich!!
If someone ever says, "Did anybody ever look back at what happened with....?" say "We did!"
Of course all those blog search engines could already be doing this, presuming they archive back at least 30 days, or someone else could build it if they provided decent APIs. Such is life.