The bitly blog examines the half-life of a shared link.
The answer? Just about 3 hours on Twitter as this great analysis from Bit.ly shows (thanks to @SBAnderson for having shared it on http://www.scoop.it/t/online-news-squared from which I re-scooped it).
This reminds me of what I once wrote on our blog here: http://blog.scoop.it/en/2011/05/31/from-melting-snow-to-snowball-effect/
For those who want to be heard, this is one of the biggest downside of Social Media today (vs Search for instance).
As Ì explained, at Scoop.it, we're firm believers that a topic-centric approach using curation can and will increase the overall lifetime of content.
What's your own experience like on that matter?