I know this is all over the web right now in the discussion about NSA and their natural hunger to collect whatever they can get their hands on. I don’t want to start a discussion on the legality or the ethnics of this, but the following slide from the EFF makes a very good point and to preserve it for my own good, here it is

see https://www.eff.org/deeplinks/2013/06/why-metadata-matters for more details…

Also very relevant is the post by Kieran Healy on “Using Metadata to find Paul Revere” here. A local copy is available here as pdf.