This has always been a major issue with social networking platforms and nothing really outrageous if you are still careful with your privacy settings. For instance with Facebook you should have your privacy set to disallow anyone but friends for everything. It doesn't eliminate all the data mining that can occur from the third party applications that people install, but that can be addressed by limiting the personal information you post on Facebook. The most personal information I have on Facebook is my e-mail address which opens me up for spam....but then that's what a spam filter is for.
However I think we are going to see an explosion of exploits from social networking sites. I just had a friend who just just down her facebook account after some of her students (she works with juvenile delinquents) managed to get some information off of her account. I believe it might have been a picture or something of that nature. These will likely be the most common types of incidents. As a result I think the teenage generation of today are going to need much thicker skin and will have to be more accepting about people's faults when voting in politicians and people in authoritative positions. It is going to be extremely hard to extinguish one's internet trail.
Online criminals target Facebook and virtual worlds (Times Online)