> I think judgment matters. If you have something that you don't want anyone to know, maybe you shouldn't be doing it in the first place. If you really need that kind of privacy, the reality is that search engines -- including Google -- do retain this information for some time and it's important, for example, that we are all subject in the United States to the Patriot Act and it is possible that all that information could be made available to the authorities.
which is entirely reasonable, yet he gets lambasted in the press as being "creepy" [2] based on a sensationalist snippet.
If you really want something to remain hidden, you have to remember that any services you use are subject to law enforcement, security breaches, bankruptcy procedures (there was a case not too long ago where a bankruptcy court judge ruled that the creditors' interests overruled the TOS and allowed the sale of information otherwise prohibited by the TOS; I can't find a link right now), etc.
With the ever-decreasing cost of mass computing, you will increasingly see just what an illusion online privacy really is.
Another example: some sites use shared avatar sites like Gravatar. I've often thought it would be trivial to crawl the Web and link identities from various forums based on using the exact same Gravatar image. In fact, someone's probably already done this.
Facial recognition is just one obvious way this will manifest itself. Another that I don't think has even been explored yet is what I would probably call "textual fingerprinting" meaning that the more you write in one post the more likely you can extract some identifiable style, choice of words and so on and that can be linked to other things you've written.
[1]: http://www.schneier.com/blog/archives/2009/12/my_reaction_to...
[2]: http://latimesblogs.latimes.com/technology/2011/01/animation...