If you really had too much time on your hands and hacking skills, you could track where anyone goes, what they buy, and how much they spend in a day. Think about it.
CVS, Kroger, and many other stores have "buyer programs" to track you.
Credit cards and banks track your spending and the credit cards know what you've bought and where.
Spy satellites can focus upon an individual and with the infaray/other spectrums, can see you in your home.
Do I care? No, because I know that for the most part I am perpetually boring and not very amusing to watch. I also don't spend very much and shop at places that do less tracking.