Another rant..
Wow as this thread highlights, this sort of thing 'privacy' seems to polarize people. With the more paranoid pointing out it may be possible to "profile" someone based on energy use, TV channels etc.. I think they are assuming that:
a) someone actually wants to find information specifically to you, the individual, and
b) its straight forward to infer personal details.
The first is extremely unlikely - think about the man hours dedicated to track one individual.
As we've seen over the past 16 years, government agencies probably have the capability to do so - but it takes a lot of resources so is reserved for those high on the 'threat' list. The only instance I can think of where more private information can be 'gleaned' from big data used by google/Facebook etc.. is if someone at the company has access to this data, and is stalking someone. Where there is a will there is a way - but that doesn't mean to say someone cares enough about you to actually find this stuff. Even then I don't think it can be done, when there are easier ways - camp outside someones house.
And the second - almost all 'big data' is owned by private firms who will not automatically roll over for a government, and it is extremely unlikely they would use 'individuals' data for their own gain. The money is in the volume, anonymized - no-one actually cares about the individual. Sure the data is sold, and I think those who generated the data (the public/consumers) should benefit from that. We do.
Where there is possible risk is if the data is leaked or hacked, because one is unsure of the motives of the hacker. But this is only for financial data (for spear phishing), and even then requires extraordinary effort to 'make use' of the personal information we give out every day.
It really does seem like those who get overly paranoid (because a little paranoia is healthy!) have a hair trigger, just waiting for stories in the news to unfold so they can justify feeling constantly scared. We don't have 'true' privacy, because it depends on what you consider to be private, but we do reap the rewards of data mining and I suspect those who are vehemently against any form of data gathering would be unwilling to give up the convenience of cell phones, the internet, credit cards, television etc.. As others have pointed out there are ways to mitigate the 'trail' we leave behind, but if that isn't enough, then you do have the choice to not use such services.