The social web can only thrive if its participants are willing
to share personal data, data about themselves, with each other.
So, you have an account with some social network (Twitter,
del.ico.us, LinkedIn, etc) in order to allow others to read your
Tweets, peruse your presentations or, quite generally, find out
who you are and what you do. With the advent of the semantic
web, of systems that can make inferences on the basis of the
data that are fed to them, this is all the more true. Individual
users profit from the services that the web offers to them,
often for free; the service providers profit, mainly from the
advertisements that accompany their services. Although there are
other business models, this is the prevailing one, it seems. So
far so good then. But what if service providers sell the data
they have acquired in the course of their business to other
providers; or worse even, what if these data end up in the hand
of others because of clumsiness (a stolen USB stick, a lost
laptop) or criminal inten