Alice Marwick provides useful thoughts on the privacy and data-mining issues surrounding the sharing of personal data on Web 2.0 apps. She shares three common “solutions” to the “problem” of teenagers’ divulgence of personal information:
1. Young people should stop putting content online.
2. Recruiters and employers shouldn’t use Google or Facebook to research potential candidates (don’t hear this one very often, although you’d think in a country where it’s illegal to ask people to include a snapshot with their resume, there might be potential room for legislation here).
3. We just have to wait until there’s no longer a divide between your “work” persona and your “life” persona. I know this sounds stupid, but I heard it from the CEO of Facebook.
Then she offers what really is happening, and what might be the best (or only) solution:
People are obfuscating personal data by using pseudonyms that can only be identified within situated, contextual networks, or by using services which allow them to restrict who can view their personal information. This is really the only one of these solutions which makes any sense.
MichaelZimmer.org 
Alas many of the people I have interviewed or whose personal blogs I have come across feel that the sheer size of the Internet is sufficient to keep their blogs from being seen in the ‘wrong’ context and it is often difficult to get the people who are your peers to sign up so they can view things you wish to keep private using technological means.
Yep, security via obscurity is long gone….
That’s actually a very old idea – basically, that it’s the individual’s responsibility to create and guard a persistent identity for socializing which can’t be linked to their job or off-line life.
Unfortunately, it’s way too complicated for 99% of users to do.
But I cannot count how many times I’ve heard it from various people from various perspectives.
You’re right Seth. I’ve been giving the supermarkets fake names & addresses for years in order to get the frequent shopper card discounts without giving them the ability to tie it all back to me.