How would you feel if you were passed over for promotion, because of the political beliefs you hold being stated in a blog comment, say? Or losing your job due to your sexual orientation, discovered from your profile on a social networking site?
That would stink - BUT - How is that different from political beliefs you stated while standing at the water cooler, or when a co-worker came over for dinner, or that were revealed by the fact that you regrularly schedule vacation days when certain protests occur, or because someone saw you on TV? How is discovering your sexual orientation on a networking site different from discovering it because a neighbor gets hired at the company, or someone you went to school with outs you to your boss, or someone you work with sees you at the mall with your date? And checking out someone's cache or search history isn't so different than checking their library book records, (and those have been used as evidence in the past).
The point is that what you do online is PUBLIC. It is just as public as what you say at work, what you do in a restaurant, where you go on vacation, or what you publish in the newspaper. And just like anything public, it is discoverable by people who weren't there at the time. Offline, we call this gossip. The only difference is the online version sticks around a lot longer. And, just to make you even more paranoid, with the proliferation of camera phones and Flickr, there are probably already pictures of you online even if you didn't post them. I don't see any way of stopping it. What are you going to do, take away everyone's cameras?
For those who are concerned that the data can be skewed to make you look guilty when you aren't, remember (1) that's been going on forever, regardless of if the data was digital or not (2) it can also be used to clear you.
The bottom line here is that we're all going to come back to a small-town level of accountability for our actions, consideration of the future implications of our actions, and honesty about who we are and what we do... even when we're miles away from home. I'm not saying if that's a good or bad thing...I suppose it will be both in different circumstances. The take-away here is don't do anything online that you wouldn't do in public, or that you wouldn't want anyone else to know you are doing. Just because you are sitting in your living room when you go online doesn't mean you aren't on the "World Wide Web" for all to see.