The last few days have linked some interesting discussions. Jill and Dennis says much of what needs to be said on this, but I'd like to add another perspective to this topic.
When doing research, we know that surveillance changes the behaviour of the research object. We also know that covert surveillance is very problematic, and there are rules about how we can use the kind of information we collect withut the knowledge of the subject. If we are not open about our role and our activities, when we publish we have to anonymize the information to the point that the objects can not be identified. Hence such inventive names as "case A" or "subject 1", and the total lack of environments and other things which can give flavour to the story. All this gives contextual information, and contextual information can be cross checked and ruin the anonymity of the research objects.
People who find themselves suddenly revealed through a study are, and have a reason to be, angry. They often feel abused and used. To reveal the secrets of another after careful study is powerabuse, the same kind of crime as rape. To hold and use certain information against another is called blackmail. It doesn't matter that the information has been gathered legitimately, if you use it to gain power over another individual, it's a crime.
As researchers we are in control, we are the ones who are gathering information. We know that we have to talk about our own behaviour, and so we are not taken by surprise when something comes up: We can't be blackmailed, we were there and were there for a reason. Armoured with a cause and armed with knowledge, we are both invulnerable and powerful.
The people who implement such things as MyBlogSpot and the changes on Facebook rarely think of themselves in the context of doing systematic information gathering along the lines of research. Truth is: that's what they do. We, the net users, don't think of the net as a field for information harvesting (for others than us). Truth is: The flow goes both ways. We don't move invisibly through the links, we leave a fine trail, much more real than pixie dust, but as intangible. Gathering information, we leave a trail of information. The ivory tower does not protect us here, and there are no sets of information gathering ethics protecting the subjects clicking on a link online. There shold be though. Information is power, and the right to gather and display information should definitely be discussed in a wide range of contexts.