all of this assumes that govs are not already trawling such online, social, exchanges
i find it strange that anyone could look at facebook (and similar) and expect privacy to be respected. by its very nature, it is not from the very start!
Private companies, and some government occupations like teachers have fired people based on their Myspace pages, and people have been arrested because of them too.
Bottom line, if you post incriminating information about yourself on the internet, you're retarded, and deserve whatever's coming to you. I find Britain's policy amusing because of their continuing policy of attempting to keep everyone under surveillance 24/7. Governments using social networking sites as a source of info is mainly a waste of their time, because few people are stupid enough to post anything incriminating, but I have no problem with them doing it beyond that. It's a public forum with no expectations of privacy.