Back in the olden days, (defined as the beginning of human communication to about 2005), 99.9% of anything you ever said or did would be quickly forgotten by anybody that heard it, yourself included. A stupid comment, tasteless joke, or even just an opinion you might later change wasn't going to derail your career or life because there were probably only a few people that heard it in the first place, and they would have forgotten about it 24 hours later. Think about the stupid things you've said or done while drinking. Odds are all the witnesses were drinking with you, so no harm no foul in most cases. Today, that lack of judgment is more likely to be a post on Facebook or Twitter, which if noticed will be quickly shared, and by the time you sober up could have been seen by millions of people.
(BTW, this is not inspired by anything that happened to me. I didn't drink anything last night!)
Social media has fundamentally changed how human communication works. Our brains have evolved to assume a certain fleeting nature to just about anything we say. If we expect our words to carry weight, like we are giving a speech or something, we typically prepare for it. However, Facebook and Twitter and all the rest archive all those fleeting thoughts, and use them to try to sell us stuff we don't need. The advertising aspects are troubling enough, but the loss of the fundamental expectation of most of what we say being forgettable is even a bigger issue. People don't change quickly, so don't expect behavioral changes to help deal with this. Having all those fleeting, disconnected thoughts floating around on the Internet is going to start biting people in the ass soon though. It already does if you are a celebrity or politician. However, imagine life insurance companies piecing together your location history from Google to decide you live a high risk lifestyle and need to pay higher insurance rates. Or health insurance companies deciding you spend too much time in bars and jacking up your insurance rates. You could be a full-time designated driver teetotaler for your spouse or friends, yet get punished because somebody figured out you are in a pub most Friday and Saturday nights from data they bought from Google.
Existing privacy laws are woefully inadequate to protect the data we consciously add to the Internet, let alone the meta-data about us that we don't even realize is being created by all these devices and services that make our lives more convenient. And given that the big companies collecting and using all this data own our government in the US, I don't see any favorable privacy protection laws in the near future.
I don't have any great answers on what you can do to combat this. I suspect the obvious things like turn off GPS on your phone, except when you actually need it for mapping services, don't do nearly as much as you'd hope to make you less traceable. Maybe looking into that is a good subject for a future blog post.